The best way to install XP SP2 is if you are reinstalling the OS. It works just fine on a clean install. However, I would disable DEP, the security center, and the Windows Firewall (if you are using a 3rd party firewall) first thing after a clean install before you install any applications or drivers. DEP has been a big compatibility problem for many apps and drivers with SP2 and I've heard it slows performance when software based DEP is used on systems that don't have a hardware DEP supported CPU. Only leave the Security center enabled if you absolutely have no idea what your doing when it comes to security. That's how I look at it anyway. I upgraded to SP2 just to have the core OS updated, bug fixes, and drivers updates. I didn't update to SP2 because of the new overly strict security BS it contains. Therefore, I disabled most of it.