this is a pretty useful guide (it is a bit outdated tho)
as for the basic steps
you need to get to a properly equipped shell (aka most of them)
knoppix or any other live CD should work, i use SUSE 10.1 install DVD and boot into recovery mode
once you are at the shell, you need to login as root and type "grub"
you are now at the grub prompt
1) find out where the grub boot files are located by typing
2) you now need to "root" into those files by typing "root (hdX,Y)
where X,Y are the numbers that you found above. X is the HD (probably 0) and Y is the partition
3) then you need to install it. do this by typing "setup (hdX)" where X is where you want it installed (look at step 2, X refers to a HD number (usually 0)) where the MBR is
assuming there were no errors, you should now be able to quit and reboot.