Hi there speedy 2004, if i connect my pc as detailed in my signature, no monitor or anything else connected, to the 500VA Belkin ups it is unable to provide sufficiemt backup power to keep the pc switched on. Your specs also look as if they're power hungry, so i would say that the 500VA Belkin ups would be unable to cope.
I have a second far less power hungry pc (2.8GHz skt478 P4, 512Mb, Geforce 2 graphics, 2 optical drives, 1 hard drive) that the 500VA Belkin can handle correctly, this is with a 19" tft monitor also connected to the ups.
As a rough guide my main pc pulls around 275W maximum under load, my second pc (which is overclocked fsb= 216MHz) and 19" tft together draw around 200W maximum.