First, most newer CPUs have CPU throttling abilities. This means that if your CPU is 2.4Ghz, it might be operating at like 1.4Ghz when not in use, to save power. Then as soon as you do something that requires more power (Like open UT), it jumps up to 2.4Ghz. The fix for this is simple.
- Adjust the shortcut in your startmenu with C:\UnrealTournament\System\UnrealTournament.exe -cpuspeed xxxx
Where xxxx is the speed in Mhz. So my 2.8Ghz Dual Core CPU is 2853 Mhz.
I suggest using CPU-Z if you are not sure just how fast your CPU is, using a value that as close as possible to the absolute MHz, the better. You may need to open Unreal Tournament, then minimize it; Then run CPUZ to get the max speed of your processor.
This second problem is with dual core CPUs. Basically there is some timing issues with Unreal Tournament and newer CPUs (dual core) and if you use AMD then you can download an easy fix.
Dual-Core Optimizer is a free utility from AMD that should help older games run better on dual core systems. You can download it here
I would also suggest getting the latest Unreal Tournament drivers. You can download the latest from this site here: