you can narrow it down, according to which OS's you want to support
when i first started writing win32 code, i tried to make programs compatible with win95, or newer OS's
it is hard to make a lot of stuff win98 compatible - even harder to make it win95 compatible
so, now, i try to make programs compatible with win 2000 or newer
if they have win2000, they must have a pentium at least

win95 will install on a 386 system (i think that's right - maybe a 486 is required)
win98 will install on a 486 system, FPU required (i know that's right)