That multicore fix seems bit different from what Toxic posted.  Toxic posted a replacement for UnrealTournament.exe.  That one seems to just start UT up using Process.exe so it's on one core.  So you can't start UT up normally using that, you have to use the icon it created on the desktop.

Download this and replace it with your UnrealTournament.exe:

http://emac.dfbgaming.com/UnrealTournament.exe

If this doesn't work then it's probably because you're not running that card on nVidia drivers.