For Future OS Re-Installs
if you're having HP pavilion Laptop, then you dont need to run FULL RECOVERY thing.
just goto HP PC Recovery app. (frm start menu) & run
Standard Recovery, it'll RE-Install only Windows XP, without affecting any files on the HDD. including C: Drive.
for clean Install, format C: Drive (using non- OEM XP CD) & run the Standard Recovery