My Computer > Special Folders
Seems they removed the ability to remap Program Files and Docs and Settings since win2k... You can move all sorts of things inside Docs and Settings, but not the base folder itself.
I guess the only choice for that is to either hack the registry or get one of those fake windows symlink creation apps and replace C:\Program Files with such a fake symlink. Personally, I prefer to leave Program Files alone and just install the better-engineered, more portable apps into D:\Programs (and games to D:\Games). Stuff that needs to be reinstalled, or can't work properly outside of C:\Program Files, gets installed in the default place.
The Documents and Settings folder is probably a better thing to move than Program Files. This site has a guide on moving such folders to a different drive, then replacing with a fake symlink for transparency:
http://sean-janus.optionpc.com/move-dirs.html