Well, here's the list of tweaks I know for MS's best OS yet and the foundation for the upcoming XP.
Starting out
If you think your existing 2k install is fubared, install a fresh copy. If you have a 9x OS, don't do an upgrade install. The install is pretty straight forward, here are the high points:
You should decide whether you want to use ACPI or not. ACPI simplifies a lot of the configuration issues with PC hardware, but is notorious for having issues of its own. Do some research at deja.com and ntcompatible.com to see if your mobo properly supports it. If it does, there is no reason not to use ACPI.
June 4, 2003 update: Almost every mobo supports ACPI perfectly. In most cases it is not advantageous to disable it.
Should you have a reason to disable ACPI, then you must hit F5 when Win2k setup starts and it says "Press F6 now if you need to use a third-party SCSI or RAID driver." Real intuitive, eh? Then you can choose Standard PC from the list.
Use NTFS as your file system unless you have a reason to use FAT32. NTFS is self-repairing and considered more reliable than FAT32. I don't like converting someone's HD from FAT32 to NTFS, so if you're starting anew, definitely go with NTFS. If you wanna save your existing data, then stay with FAT32.
Order I install stuff:
1. OS: Win2k
2. Latest service pack: SP3
3. DirectX: DX 9
4. Vid driver: Det 12.41
5. MB driver: VIA 4-in-1's (w/o IDE driver, MS's is better)
Mobo drivers get installed last because SP2 has better Via support.
Reboot after installing each of those. Grand Masta D bragged he could install all of that with only one reboot, so he tried and rebooted to a BSOD. VGX. For your other devices install drivers and reboot when prompted.
The best thing to do is make a folder in your main hard drive and call it "Archive". Put all your drivers and stuff in there. I got into this habit and now I have every Detonator driver released since 5.32

. But it is very handy.
Basic tweaks
Right now, your OS is clean. Check the memory usage in task manager. It should be around 55MB right after boot, with some service tweaking you can get it down to 46MB.
Go to device manager. A very quick way to get there that you might not know is by right clicking on my computer, and then choose manage. It opens up the Computer Management snap-in for the management console. This is the heart of your OS in one place, its pretty sweet.
Enable DMA on your IDE drives by expanding the IDE/ATAPI tree. Double click on the Primary IDE controller and choose Advanced Settings. These are the drives hooked up to your IDE chains on the computer. If the device type field is not grayed out, that means there isn't a device there. Change the device type to "None" and Win2k will not try to autodetect devices on boot, saving some time. Otherwise, if it is grayed out, verify that the Transfer Mode is set to DMA if available. DMA greatly speeds up disk performance and makes the computer more responsive. Do the same procedure on the Second IDE Channel. Reboot if any changes were made.
If you have a PS/2 mouse, note that it has an advanced properties page (in device manager) that lets you change the sampling rate on the mouse to 100hz and smooth it out.
Right click on your desktop, go to the settings tab, now click advanced. Go to the troubleshooting tab and move the graphics acceleration down one notch. It's been shown to actually increase performance.
Now go to the Sounds and Multimedia control panel. Click the audio tab, then click settings for sound playback. Ensure the speaker setup matches yours, and click performance. Move the slider to the far right. If you get glitchy sound, come back and move it one notch from the right. Click OK. Max out the acceleration for recording as well.
Advanced tweaks
Download the
DirectX control panel and install it by unzipping it into c:\winnt\system32\ folder. Go to the control panels folder and open the DirectX control panel. Click on DirectSound and move the debug level slider to the far left.
Get
TweakUI 1.33. Extract the contents to a directory, and then right click on the tweakui.inf file and choose install. Go to the control panel and load TweakUI. It has a ton of useful options, one of the best ones is allowing you to disable Active Desktop. AD has been known to eat memory since Win98, so make sure it's off, then untick "allow active desktop to be turned off/on" and "allow changes to active desktop." Everything else is just preference.
Get the
Extensible Counter List Utility from MS. What performance counters do is monitor the performance of various aspects of your computer, most of which you probably don't care about. Run it, and sort by counter ID. For each counter listed in the box, click it, and untick the "Performance counters enabled" checkbox.
June 4th, 2003: disabling performance counters can cause more problems than the incredibly miniscule gains it can bring, so I don't recommend this. In particular, users installing Visual Studio 6.0 may have difficulties with some utilities included with it.
If you have an Nvidia-based card:
Right click on the desktop, click properties, then settings, then the advanced button, [vid card] options, click additional options. For 12.xx drivers, start with the Antialiasing tab, and choose to "Specify an antialiasing mode," and then choose Off. Under OpenGL, tick the first three boxes in the listview at the top, v-sync always off, use desktop color depth.
Download
NVMax final release.
Set your OpenGL misc tab up like so:
Addendum #1:
Here are the services I have set to start up automatically:
BE SURE TO LEAVE PROTECTED STORAGE ON AUTOMATIC
Addendum #2:
Updated the services to show ones that I disable, and set a lot more of them to manual. You may want to check out the changes. I don't share files out, if you do, set the Server service to automatic. If you don't have a Zip drive, you may set the removable storage service to manual. Everything else is pretty essential, or gets started at boot regardless of being on manual or automatic. Note you CANNOT sidestep this by disabling them, you'll end up with a system that refuses to boot

.
Messenger service is disabled because it will receive messages from people on your LAN that steal focus from what you're doing. I've crashed people's computers sending them a message while in T2, since it handles alt-tabbing so gracefully.
Remote Registry Service is disabled cuz I just don't like the idea of it.
Routing and Remote Access and the Utility Manager are both disabled because I have absolutely no use for them. Disabling the Utility Manager frees up the binding on Windows key-U.
Registry hacks
Not for the faint of heart. Also, don't try these on 98/ME/NT4. If you screw up you can render your computer inoperable, etc. In case you do, hit F8 when you boot up and choose "Last Known Good Configuration." If you're in doubt about something, then
don't do it. Milliseconds and fps gained can never replace time spent restoring your system.
Still with me? I thought so. Start, Run, type "regedit". Open the key: HKEY_LOCAL_MACHINE \SOFTWARE \Microsoft \Windows \CurrentVersion \Explorer \RemoteComputer \NameSpace \
and delete the branch:
{D6277990-4C6A-11CF-8D87-00AA0060F5BF}
Banshee. (note the period

) told me about this and it REALLY speeds up browsing the network. A bug in Win2k causes it to search for scheduled tasks on remote computers, resulting in a delay of up to 30 seconds when browsing other the network.
HKEY_LOCAL_MACHINE \SYSTEM \CurrentControlSet \Control \FileSystem
Add a value of type DWORD named "DisableLastAccessUpd ate" (no quotes) and set the data to "1" (no quotes) to prevent NT from tracking every single time a file is accessed.
More to come if I can find the other ones.
antareus
(05/02/02 Edit: NVmax link updated)
(06/04/03 Edit: more opinions, the guide is close to stale now. Someone want to make a new one?)