If you have a bit of an oddball machine or a current machine with known issues with SP2, try creating a slipstreamed CD using your XP install CD or restore/reinstallation CD. I've had very good luck with installing SP2 using this method. Yes it does mean reformatting the HD and reinstalling all the software and personal files after the OS is reinstalled, but when finished I end up with a rock solid XP SP2.
Note: if your machine has a Prescott or Pentium M processor then you may have specific issues relating to the CPU speed settings. You'll need to research this for your machine and apply the necessary updates/tweaks to fix it.