Hi flobby, sounds to me more like a processor or memory problem than one with your monitor refresh rate. Inadequate refresh rates manifest as a constant flickering on the screen rather than the 'stuttering' I think you are refering to.
The most likely problem is your processor is having to 'catch-up'. XP pro has lots of processes running in the background. Just press Cntr-Alt-Del and clicking the processes tag and you can see just how many. In addition, as the OS is writing and reading to and from the hard disk and/or CD, this too uses processor power. If you are unhappy closing processes, and you should be as some are essential to windows, I would suggest downloading a copy of 'TweakXP' from the net and getting that to tweak your settings for you.
Hope this helps.