I have a triple boot computer, so I can compare the three OS: Win2k-Pro, Win98SE, WinXP-Pro.
Win2k and WinXP are significantly faster than Win98, even on an "old" machine (PIII-450). They are more stable and almost never crash. Microsoft almost ended support for Win98 (which they are sure to do in another year or two).
If you still like Win98, create a dual-boot, and choose which OS you want when the computer turns on.