I have a weak pentium4 3.0 GHz, 2 GB ram and a 512 MB 7600gs that I overclocked. The processor is the main thing that gets in my way. I have a 19 inch 4:3 monitor and a 58 inch 1080p DLP tv that I use over HDMI.
When I play at 1280 x 720 on medium there is choppiness at times but it doesn't...