I friend of mine has win Xp installed but when the system has booted we
the a lot of mysterious errors related to browser and files that wants
to be reinstalled. After a while Win Xp reboots automatically.

I tried to install win Xp (Home) again but I get the same errors.

Do I need to reformat HD? What is the best way to do it? ( 200 gb)
What tools do I need to use when I format? And how shall I format the HD?

All hints welcome.