I agree; running my IntelliMouse Explorer through the serial port crashed my OS (Win98 2nd Edit.), works great through the USB port (driver ver 4.10.2222, if I'm looking in the right spot).  I haven't tried booting my computer into safe mode yet, though:)
--alex

Bruce after Stan writes:
Let me de-recommend the Microsoft "IntelliEye" mouse, with or without the extra
buttons. It has problems tracking at high speeds; it appears to "get lost" and
quit sending when it's moved rapidly across a surface. I originally thought
that the problem was with the Macintosh mouse drivers for it, but I've since
found that it has exactly the same problem on WinNT and Win98. If you're a slow
mouser, you may not notice it, but if you're used to making very rapid mouse
movements you're likely to find the IntelliEye behavior pretty irritating.
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