I recently updated my Media Center to Vista; my GeForce 4 was replaced with a GeForce FX5200.

I kept getting a flickering screen when using the Microsoft drivers; it wasn't handling TV output properly.

I went to nVidia's site to get the (bad!) drivers... and I have my AGP nVidia GeForce FX5200 running ForceWare 97.46.  I selected (manually, using Have Disk) to use this driver instead of the OOBE drivers that ship with Vista.

Now to fire up Media Center...

Update: It works.  GeForce FX5200 on ForceWare 97.46 (which are supposedly for GeForce 6/7 and FX6000+) is WORKING for Vista Media Center, and Aero.  DVD playback and TV live playback is fully functional.  I don't play games on this thing... so... =) I'm not going to bother testing it.