I guess the issue is just that Windows re-writes the MBR. I don't quite follow why suse didn't put grub in the MBR, and I'm a bit confused as to how things stand from your description.
So, what I would do is either boot suse and reinstall grub with
grub-install /dev/sda (assuming sda is the correct device), or if you can't boot suse, boot the dvd into rescue mode (I guess it has a rescue/repair boot option), or download a live CD of some kind, then mount the hard disk partition with sus on it (say /mnt) then
grub-install --root-directory=/mnt /dev/sda