I don't think this is a Windows 7 problem. If I'm remembering correctly, the original game had the same problem in Windows 98 and XP. It happened if you had collected "too many" photographs within the game. The solution was to delete some of the photographs (while in the game). Then you'd be able to save again.
I don't remember if the patch addressed the problem. The description of the patch at
***Gamershell*** doesn't mention it, so the saving problem might have been left unpatched. If you have a recent version of the game, it should already be patched.