I have ubuntu 8.10 & Windows XP installed on my PC. I formatted the C:\ partition and installed a new fresh copy of Win XP.
After that I was not able to login to ubuntu 8.10. It is clear that Win XP overwrote the MBR.
I tried to re-install the boot loader (Grub) again by boot ubuntu 10.10 CD. Finally, I was able to boot both ubuntu version 8.10 and 10.10. However, I was not able to boot Win XP.
There is an entry in grun menu of ubuntu 10.10 specific for WinXP, but when I press enter to boot Windows I get back to grub menu.