Thats right. Boot with slackware and say grubconfig.
In Fedora, may be you could boot in rescue mode and say grub-install.
But I had a weird one while rescuing grub once in my friend's computer. I am going to get blasted for this, but here it comes anyway
. WinXP did not overwrite the bootloader. It commented (!) the grub.conf file where it said boot from hda. On uncommenting, it started to show the grub menu, with fedora and xp in it.