Do you have any boot options at present? Does GRUB (or Lilo) appear when you boot the system?
If not, I think you can create a MBR by booting the pc into Linux using the Linux installation CD. When up and running, YAST has an option to create a new GRUB. It should be able to recognise the operating systems present on your pc and configure appropriately.
Hope this is right as I am doing this from memory based on a similar problem a year or so ago.