I found a way to edit the Places Bar (You know, the folders on the left side of the open and save dialog) in XP and it works for Vista as well. Basically go here…
HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersion Policiescomdlg32Placesbar
…and edit the locations; DWORDS are common locations, so you'll have to look them up, but strings are just paths to folders. The max is 5 (Place0 through Place4). Here's a link to an article describing it.