I know that some time in past Capcom launched 3 or more versions of Street Fighter 2 for PCs. Certally I knew Super Street Fighter II Turbo and Street Fighter Alpha for PCs.
I searched around entire world looking for legal copies of these games, and didnt found nothing. I found only some results in eBay and a website that sells sealed "abandonwares", but I`m quite distrusted about this seller`s game authenticity. (I dont know if I will received an original cd, a cloned CD, floppy drive, or an emulated application).
Gog.com already tried to talk with Capcom?
(Already tried to talk with Team17 to offer all Worms collection to us too? =)
Thanks a lot!

how about Konami to offer us old versions of the silent hill games?

Or that Konami Collection for Windows???

Yes! The entire Team17 catalog on GOG, please! :-D

I bought Super Street Fighter II Turbo in the bargain bin at a place I used to work at about 8 years ago. It was a whopping $1.99. Even came packaged with a controller! I never opened it though, so it's just sitting in my collection :P
Also found a copy of Mega Man 3 on PC (on floppy disks, no less) that same day.

Or just download Super Street Fighter II Turbo HD Remix. The mechanics are a little antiquated and limited compared to the Alpha games, but it's still fun for a few rounds. Not to mention the online mode which should extend that game's life shelf tiding us over until Street Fighter IV comes out.
Seriously though, there are so many versions of Street Fighter out there I don't know why you're bothering to track down a PC version. If anything, at least find the SNES versions.