well first of all just to get this outa the way......www.google.com, ok now that that is outa the way heres a couple good ones i found
-Mac Os on windows/ www.emulators.com
-neogeo for windows/ www.emuunlin.com
-Playstation for windows/ www.emulator-zone.com/doc.php/psx/
-SNES for windows/ www.snes9x.com
/free/ dont get zsnes, its really gay and alotta times can hold trojans
-Sega Genesis for windows/ www.emulator-zone.com/doc.php/genesis
these are some of them out there, most emulators u find will run in DOS, so i dont know if they work with XP or anything so just test em and find out.