OEM means Original Equipment Manufacturer, its just a meaningless way of explaining that the Hard drive is by itself with no cables, no retail box (Just a basic cardboard unit w/o anything written on it), no instructions, no manual, no cd, nothing but the hard drive.
SATA is the next generation of cable for your pc, its much smaller than the big fat flat IDE cable, and offers a higher speed transfer rate between the mobo and the drive(s). SATA is replacing IDE. You don't want or need it b/c your mobo probably doesn't even support it (Need your mobo specs and model #), it won't make your pc or drives run any faster unless you are doing a raid array with like 2 WD 10000 rpm 80 gig raptor drives. I use two SATA drives b/c my mobo supports it. In terms of upgradablity I would wait and buy a new PC at the end of this year instead of upgrading anything because by that time the standard ATX case will be replaced, PCI express will be out, ddr2 (and maybe even ddr3, or quad channel super high rate RDRam) will be out, 64 bit processors will be mainstream, and SATA will be mainstream. Buying a computer, or upgrading a PC in the mean time will be a futile endeavor. THere hasn't been this much turmoil in the hardware market for probably more than ten years, its a good idea to wait to purchase.
