How do I reformat my hard drive? (windows XP, NTFS Harddrive)

I need to reformat my harddrive… it has been shutting down crashing freezing etc… I have backed up the data I want… so what do I do next?

OS: Windows XP

HD: NTFS

thx…

Edit: I now have the professional SUSE Linux software and Im planning on installing it… but I want to have windows XP on the copmputer also… does anyone know how to install two operating systems on one harddrive? or two?

I have one Internal 40 GB HD and one external 80 GB HD… thx

~psych