err No they dont. Nearly all programs these days require Windows XP. I havent seen new software come out for years that supports Windows 98, as it is ridiculously old (Heck, its not even supported as a "Legacy" product). While a few things ask for 2000 SP4, a lot more want XP/XPSP2, however the CPU requirement is about right, although enough stuff asks for 2.0Ghz or higher even if it doesnt need it.
a lot of current versions of win32 apps run on 9x.
opera and kmeleon run on win9x, though opera 9 was the last i
personally ran on 350mhz k6-2 (cheesier than pII based celeron) win98se. opera 10 and 11 seem significantly more bloated. kmeleon might have been 1.5.3, little different from current kmeleon.
i don't use 9x anymore, but read about it (interest? amusement?)
check the unofficial 9x area of msfn. also "kernelex". Without kernelex, the biggest lack is av -- afaik, 9x will run only clamwin (optionally with sentinel).
2k
i think there are similar 'unofficial' support/patch people for win2k.
xp
just a hunch, but xp
sp2 requirement might be for .net apps. (digression. ms updates require sp3 for x86 or sp2 for 64bit.)
as with other oses, win apps tend to need ram, rather than cpu *hz.
yt vids are small, so no trouble for old pcs.
avoid startup lag by avoiding startup scan option of retail security bloatware, or stay with original size hdd .
earlier p3 (pc100, like a g3 or early g4), xp, 512+mb: sketchup7, 2d cad, but true rendering (kerkythea) is hopeless :-/