I recently came across Retrospec, a group of hobbyists dedicated to recreating classic Spectrum and Commodore 64 games.
They have several completes games available on their website, including one of my all-time-favourites, Head Over Heels. I'm happy to report that Head Over Heels works well on Vista! :)
Then of course, there are emulators that let you run the original C64 and Speccy games on your PC. Some quick links: Gamebase64, Lemon64, C64.com, VICE
Somehow I'm more inclined to play remakes of the classic games that use the improved graphics and sound capabilities of modern PC's, but every now and then it's fun to fire up the originals and bask in their SID-tuney glory!