technically, yes, the ultra66/100 drives are backwards compatible. since you are running on an older board, however, go to the manufacturer's website and check for updated bios. often you need an update to support new drives, not because of the 66/100 interface, necessarily, but the fact that they are >8GB in size. i spent 4 hours one night wrestling with adding a new maxtor 40GB drive into a little bit older celeron system. had problems detecting on boot, no matter what the jumpers and compatibility modes i set. THEN i checked the website and found the bios was 2 years out of date. after that update, all worked flawlessly.
lesson: whenever upgrading a system with new hardware, check mb manufacturer for updated bios BEFORE hooking anything up.
if you haven't purchased a drive yet, i would recommend the maxtor diamondplus 60 series, 40GB in size. search pricewatch.com for "5T040H4", which is the part #.
--froppy1