i dnt understand one thing why u people need to install GRUB in the MBR(master boot loader). Its a common problem when u try to boot from XP cd nd GRUB dnt allow u to do this. One shud make ur PC dual boot for both linux and windows.. then u dnt have to face such problems..there are three processes by which u can use Ntldr for deciding the menu for OS..u dnt have to give the whole power to GRUB. The three processes are:-
1)Use dd to copy GRUB stage1 to a binary file
2) use BOOTPART command
3) use GRUB for DOS application
but itz ok...i think there is no point in mentioning all these things over here..i will write an article on that so that no computer user has to face such problem in future regarding GRUB. Now for ur case try vista, windows 7 etc etc nd finally if u cnt do nething then full format ur computer...