I left win98 1999 for win2k beta and never looked back.
after that i switched to whistler beta and im now using xp.
The main reason i have stayed with xppro is the support for Hyper Threading Technology and the
performance benifit that comes with HT! Wiin98 dosent have any smp support at all...while in 2k it can work (seems to depend on the mobo/bios but generally not recommended to run a ht enabled wk box) not as good as in winxp though.
Overall XP OWNS any other previos version of windows completely, IMO there not much of a option here go with XP if you have a P4C chip. If you have Athlon64/p4b/p4a then go with 2kpro/xppro or even win98se
-ntrights
edit: added win98 to the last line