if you have a 3rd drive configured its ..easy ..just store all important files and data on that..
but cause you have operation system in 2 of them ..will be a little tricky ...
you need a installation cd with xp on ...its better than vista in my opinion..,and boot from it to be able to format partitions after loading primordial files..and agree with the license ..
if you only have 2 partitions...let the important files in the first one..C..than boot from cd ..and go with the installation until you get to the previous instalations...after that choose the D partition ..and delete it and rebuilt it ...and stop here ...
reboot your computer and will boot from the C partition with the windows you have there ..
in this point go to my computer ...and click on D and it will ask you to format cause it is row ...yet
after format it ...just move the important files to it ...and again boot from cd ..and make a clean installation in C drive ..with complete format in NTFS ......choose esc when it asks...I mean not to repair ..and make a clean installation ..and let it so ,, with just one operation system ..
the reason I guided you like this ..cause from windows you will not be able to format any partition containing boot scripts..and operation system..
let me know if you got the point ..and if you do not have a good XP sp2 (genuine and update-able to sp3)
here is where you can download form torrent an image which once burned directly by double clicking on it..(and using NERO as file associations program) will end up with a great XP bootable..http://thepiratebay.org/torrent/5388204/Windows_Xp_Genuine
remember you need a torrent client program to download...(bit torrent , lime, utorrent...and so on ...)
and NERO or Iso burn ..to burn it .., and to end up bootable ..it enough to have the burner installed..and clik double on the image file to start burning..(use a new CD-R )
please to not forget to rate if helpful...