1) Create a partition for OpenSuse (if you don't already have one)
2) Install suse to that partition
3) When asked to install the bootloader, choose to install it to the / (root) partition,
not the mbr
4) Reboot.
5) See if there is a choice in your grub boot menu. Grub may or may not automagically find the suse partition. If it does, your done. If it doesn't, boot to ubuntu and follow the instructions on
this page to add it.
Good luck and post back if you hit a snag!