You need to reinstall the GRUB boot loader, so that there is something that can actually get SUSE started. In order to reinstall the boot loader, you need to first boot into a Linux Live CD or some other Linux environment. Once you have, you should be able to go to a terminal and do something like:
Code:
grub-install /dev/sda
(This assumes that you only have one hard disk and that you want to install GRUB on the MBR of this disk)
Once GRUB is installed, you can try rebooting. There's a fair chance that the newly installed GRUB will pick up and find the old GRUB settings for SUSE and boot normally. If it doesn't, you will still have a GRUB command line which you can boot SUSE or Windows from temporarily if you know the right commands.
It is difficult, however, to explain what the right commands are going to be without more in-depth information about this particular system -- how many drives are there? What partition layout is on the disks?
If you have GRUB installed and are getting stuck at the grub> prompt and don't know what to type, you can restore access to Windows XP again by booting from a Windows XP CD and choosing the Repair option. When you get to the Windows command line, type fixmbr and press Enter. This deletes GRUB and restores you back to the situation you are in at the moment -- Windows XP should then boot normally.
