I haven't tried playing UT2003 with lower settings because I have been running the game (and many others) with no problems for the past 2 years. The only changes I have made the the system is when I updated the video card for a 9800 pro a week after I got the machine (the one in it was gash), and added 512mb ram which I've had to take out due to a fault on Memtest86, unfortunataly this wan't causing my fault.
I will take your advice and see if i can borrow a PSU and GFX card.
Any recommedations for a PSU and Video Card if I need new?