One of the biggest problems people seem to have with dual booting is installing the bootloader. Decide which distro you want to boot. If you want to boot with opensuse, install ubuntu first and when it asks where you want to install Grub, install to boot partition of root drive NOT the MBR. When you install opensuse, install Grub to the MBR. Note which partition your initial install is on so you don't overwrite with the second installataion. You only need one swap partition (probably don't even need one if you have 1GB or more of RAM and you do not do any intensive graphics or gaming).
I would suggest you take some notes during the installation process as to what screens you see and what is being done in each step so if something goes wrong you will not repeat mistakes. If everything goes right, you will know how to do it the next time.
I'm surprised your opensuse didn't detect the already installed ubuntu as I just installed opensuse a few months ago and had ubuntu which was detected. Oh well?
Post again if you have problems. Good Luck.
Googled a little for booting multiple Linux distros but didn't find much.
Last edited by yancek; 06-11-2008 at 12:39 AM.