do one thing man, to restore the MBR for just booting windows, thrown in that Windows XP CD and boot from it, and choose to repair the install pressing 'R' key when asked for. and this will ask u for the Administrators password and then u will get at a command prompt like

C:\ WINDOWS\

so here u just type 'fixboot' - this will rewrite a new MBR and this will make only the C partition with Windows XP bootable and just type 'exit' and restart and everything shud be fine, let us know how it goes. u might wanna reformat the other partition from inside Windows XP, using computer management from administrative tools !

cheers....

newNovice.