Ok people its not the game thats messed up if your having problems with it its your bios configuration that in return makes UT3 gameplay choppy and creates low framerates. Epic can't recreate your problems wonder why??? It has nothing to do with the game or Vista it's your IRQ Resources. A old solution to a new problem. In your bios make sure your Video Card unless in SLI mode, Hardrives, Ram, Network Cards, and Soundcards don't share the same IRQ. It can be changed from your bios and you can see what Device uses what IRQ in Device Manager. Go to Device Manager Click View and select Reseources by type then double click interrupt request section. When you do this you should be able to see what your devices irq's are and if they are sharing, if they are sharing irq's like a hardrive and a soundcard share irq 6, which was my problem either move the sound card over a slot in the motherboard. or disable devices on your motherboard to free up irq's so the device that is using the cpu more can have it own irq like disabling the serial com port, or the ecp printer port, or even the firewire port. Sharing a Harddrive with USB irq is ok just make sure you share a device that uses the cpu a lot with a device that doesn't use the cpu that much.
Just follow these steps and your gaming will be smooth as butter
Fix also works for Gears of War will post in other forum soon
The irq's are also viewable when your computer is booting but only for a split second in the lower right hand corner of your screen.