I currently have the Sims 2 with the University, Nightlife and Seasons expansion packs installed. I recently started downloading items and Sims from the exchange on thesims2.com. I downloaded several lots a few weeks ago and have had no problems. Then, today, I downloaded some objects and a few sims. Things were fine at first, and then I downloaded about a dozen more sims. Now the game crashes every time I try to run it. I've tried with custom content disabled, and with it enabled. It doesn't make any difference -- it crashes either way.

At first it was fine until I tried to create a new family -- it would let me enter the family name but then crash as soon as I hit the button to add a new sim. Now, the game will enter the neighborhood, but crash as soon as I hit the button to simply display the Sims I already have.

If disabling the custom content doesn't work, I'm clueless as to what to do about this problem. Do I need to uninstall and then reinstall? I'd rather avoid that if possible, because I've put a lot of time into the families that I already have.

Help would be much appreciated!

It sounds like a reinstall would be in order, or check for updates or patches.
I don't know anything about that game in particular but a lot of games have a file or folder that you can save that contains your games. So you can make a backup or copy of the folder then reinstall the game and copy the backed up files back to the original location. Ask on a forum particular to that game, I'm sure your not the only one that has had these issues.