Is your XP or vista’s bootloader is crached due to Linux installation or some other mes up..
Dont worry..jus follow the following steps to recover….
after booting hit ” r ” to enter Recovery Console
from there Hit ” 1 ” to enter C:\Windows\> if you have Administrator password enter it if no password then just hit Enter
now type in the following commands
then type EXIT to reboot
now eject ur XP CD
now ur Windows XP should boot properly ….
Tested in windows Vista too…..