Windows XP won't let you format your C: drive from within Windows XP. Microsoft put in "suicide" prevention basically that kept people from accidentally formatting the C: drive, now Windows is smart ...
I'm changing a HDD on a Compaq machine (from the original 30GB to a used 160GB Barracuda) and during the XP setup phase, it's taking an unusually long time to perform an HD format (not quick format) ...