Also, the Sims save files like to grow to as much as 500 MB. :/

But yeah, it rebooting in safe mode to delete it sounds like a plan. In order to do that, you need to press F8 right before the Windows loading screen appears, and select safe mode from the list.

I also remember the Sims 2 having problems with save files and expansion packs, but that might be unrelated. In either case, the save files should be in a sub folder in My Documents. It shouldn't be to hard to figure out which folder it is, I remember it being properly labelled.