as if you don't know.
HP2: system hog, required a Geforce 4 ti 4200 that too without aa, couple it with a 2.2ghz
U2: atleast a 6600GT to play at 1024*768 MAX AF, no aa
MW: stutters badly even with a 7600GT that too at any res, though you do run it at 10X7 MAX AF, no aa, it is going to stutter on each setting, so why not let it stutter with eyecandy.
MY ESTIMATE
GPU: 7900GT or X1800XT at the minimum will be required to play at 10X7 MAX AF, no aa
RAM: Upto 2gb
Cpu: Probably Amd 64bit 4000/3700 or equivalent, a winchester/venice at 2.4-2.6 may be fine.
even UT04 had same engine as UT03, while a mx 440 64bit or at most 64/128mb geforce 4 ti 4200 may have been fine with UT03, to play UT04 at max, it is more like 9700 class or atleast 9600pro /xt, don't know for sure.