Rebuilding PC

I have a PC running two operating systems on ot WINDOWS XP and WINDOWS 2000. for some time now it has sarted cretaed problems and runs very very slow now. I wnat to clean everything on the harddisk and just install Windows 2000 opwerating system. I do not know how to go about it. I tried to boot through Dos Boot disk but didn’t work . Tried Fdisk didn’t work. Can someone please tell me the precise method of just cleaning everything off the HD and frsh install just one operating system.

look forward to hear from someone soon.

Thanks in advance

Ash Tamhane