So did you make a boot disk that contains grub? Or did you install grub to the MBR of the disk that bios boots from? Grub is actually very easy to use. You need to know your disk partition tables and where the OS you want to boot are installed. When you start the computer, I am assuming that you are not getting a the list that says which system you want to boot on your computer. You are getting a grub> prompt though, right? Well then define your root by entering root(hd0,0) where you can change 0 and 0 to represent different partitions on different drives. Grub counts from zero so your first hd, which is normally hda, is actually 0. Partitions are also counted from zero.
Ex: First partition second hard disk:
grub>root(hd1,0) (the second hard disk is 1 and the first partition is 0 ... now if your system is on an extended partition, those automatically count from 4, I think, regardless of how many primary partitions you have.)
Now that root is defined, enter the kernel you want to use. Usually your kernel is located in /boot/ so type in
grub>kernel /boot/vmlinuz ro root=/dev/hdb1 where vmlinuz is the kernel you want to use, ro is read only and root defines your root partition, which will match your first entry always (I think). Now Grub is COOL because it will let you see what your options are concerning kernels. That is type kernel /boot/ and then hit tab and it should give you a list of the stuff in /boot/ ! Actually hitting tab is helpful for figuring out root too. Try it and youll see.
And you are up and running. Then make sure to edit the grub menu which will probably be in /boot/grub/ or not...depends on your system I guess.
The file is called menu.lst
color green/black light-green/black
kernel /boot/vmlinuz-2.6.3 ro root=/dev/hdf6
title Windows 2000
Note: You can use the Windows entries above to boot windows if you want too. Just enter grub>boot after entering the three commands above (separately!)
Finally, if you dont understand the naming system for your hd's, you should just try different root entries at first until you find the correct one for grub to work. It shouldnt do anything harmful (just a guess though!)