ok - have a look at downloading gibraltar2.0 from gribraltar.at
that will give you a good linux enviroment to rescue your sytem.
i dont know out of the back of my head on how to get your boodsector backedup but search on www.google.com/linux
for 'backup bootsector' or 'dd hda' (dd is the command you would use to take a backup of your bootsector)
from a gib. booted sys you could mount your partitions in the correct order, and chroot into you enviroment and run grub-install from there (not sure if this will work)
or have a look at knoppix or any other live-cd's