I started out with Windows 98 on my first computer (I still have it, but the hard drive crashed yesterday. :'( )
I got another computer with Windows 98 back in 2001, upgraded it to XP. Talk to me about spyware, that thing could barely boot. It died in 2006.
Got a Mac Mini, had Mac OS X 10.4 on it (PowerPC) (Still have it)
Got a Compaq Presario C300, the worst laptop I've ever used, had XP. (Died in October 2008)
Got a Dell Optiplex 320 (my current computer), with Windows XP on it. Upgraded it later on to Vista.
Got an Asus Eee PC 701 in July 2008, with XP.
Then, just recently, I was given a Gateway M675PRR. Installed Ubuntu Linux and Windows XP on it.
So, in conclusion, yeah. I used Windows 98, Windows XP, Windows Vista, Ubuntu Linux, Mac OS X 10.4.