well, idk of any cdrw drive that will burn at 40x, but whatever...
Try upgrading nero to version 6 I think?? It will use your old cd key to do it, if not then gimme a hola on PM.
The proceedure I use when I burn a disc:
1. Listen to all mp3 files so you know for fact that they dont have errors
2. Ensure bit rates are compatible with nero ie 128, 160, 256, 320 etc
3. Shut down all other back ground programs
4. Start nero and make a compilation out of the mp3's check to make sure you aren't trying to burn more than the disc can hold in BOTH space and time wise.
5. Test the disc bring first at the slowest speed and work up from there until u find the fastest speed at which you can burn without making a coaster.
6. Burn disc
The process becomes expedited after you get the hang of it and you can delete some of those steps.
Check to make sure Nero recognizes the proper drive, and get nero to benchmark the drive.