Ack, and if the first thing doesn't work, before repairing Windows using the disk, try this: http://support.microsoft.com/kb/304449/

Oh, and if that doesn't work, use your install disk to repair Windows (not in the recovery console). It'll reinstall Windows and should do the trick.

Hit F8 when booting. Try choosing "Use last known good configuration."

Have you tried removing the new card? That stop error is frequently caused by faulty drivers.