I have a very similar spec machine, and although I don't get great frame rates I don't recall it pausing/skipping. Normally run Linux on this machine and don't know if I tried the beta1 on it, so I'll give is a special boot into WinXP during the week and let you know....
Most likely there is something else on that machine which is causing the processor or disk to be 'distracted', can you try to shut off any other programmes to see if that makes a difference.
Simon.