NO.. I own an Optiplex gx280, as area 51 said it is P4 HT only not a 64 bit one..
i tried installing 32 bit windows, installation ok. but no video drivers for win 7 and as a result performance is really annoying, i tried adding HD5450 Low Profile (no power pins required)..
the gpu reached 60-65 degrees within 5mins of operation & PSU is pushing so much heat.. so i removed HD5450 & win 7 & switched back to win XP..
The PSU is not enough to juice to power seperate gpu, if you have small mini tower type you can succeed with HD5450 or othe low end GPUs ..
FYI my GX280 is SD (Small Desktop Form factor)