It's official via a press release. 
Midway and Epic today announced the minimum and recommended system requirements for the PC version of Unreal Tournament 3, the highly anticipated first-person shooter scheduled for release in November 2007. Please see below for all information regarding these requirements along with newly released screenshots from the PC version of Unreal Tournament 3. 

Minimum System Requirements 
Windows XP SP2 or Windows Vista 
2.0+ GHZ Single Core Processor 
512 Mbytes of System RAM 
NVIDIA 6200+ or ATI Radeon 9600+ Video Card 
8 GB of Free Hard Drive Space 

Recommended System Requirements 
2.4+ GHZ Dual Core Processor 
1 GBytes of System RAM 
NVIDIA 7800GTX+ or ATI x1300+ Video Card  
8 GB of Free Hard Drive Space  

NOTE:  Recommended  (x1300 possible typo - x1800 more likely) as the x1300 is pretty much the same as the 9600 that they have listed in the minimum requirements.