Reinstalling grub
 

I had a dual boot windows xp/fedora core2 and it work fine until one day windows decided to crash and i had to reinstall it again but doin so it erase the mbr and grub and know i can't use linux because it boots automatically for windows.How can i reinstall grub and fix this?? thanks

This is a good place to start.

http://www.gnu.org/software/grub/manual/grub.html

Use your FC2 installation cd to boot (just like when you installed and look for 'rescue' instructions in the boot screen.

Once you're inside your system, you'll have to chroot (change root) to the partition your original root was on (e.g. /dev/hda3) and just to make sure the right /boot partition is mounted you might want to
$ umount /boot
$ mount -a /boot
then reinstall grub with
$ grub-install /dev/hda

Another option for you - Booting Linux with the NT Loader.