DEP software is already included with WinXP SP2. You can find the options in System Properties -> Advanced -> Performance Setting/Options -> Data Execution Prevention (DEP).
Maybe this is what makes XP2 so slow when executing apps etc? I've just started investigating the new features in SP2...
I guess the "/NoExecute=OptIn" option enables software DEP. Have someone tried switching it off? Maybe I'll try that later and see if it solves my slow app executing...
/Cthugha