How do i format my basic hard disk from windows mode

Do you have your windows CD?

What is your goal?

From Windows you can format partitions other than the system partition (usually C: ) via Disk Management. Right click My Computer then click Manage then Disk Management. Right click the drive or partition and choose Format...

You cannot format the system drive or partition from Windows.

If you want to reinstall XP then as Wikety says you need to boot your XP CD.

Also understand that if you format your boot drive, you will lose all your data, your email, favorites/bookmarks, downloaded files, updates to them, and you will end up months, or even years behind in critical security updates.

If you are having problems with your computer, note that formatting and reinstalling is always the last resort.