The simplest thing to have done would have been to install the Opensuse Grub bootloader to its partition rather than the master boot record, then run update-grub from Ubuntu. Apparently, you didn't do any research on the difference in the bootloaders prior to the Opensuse install?
You can boot Ubuntu from Opensuse by putting an entry in the Opensuse menu.lst file which is in the /boot/grub directory. An example if Ubuntu is on sda5:
If your Ubuntu install is not on sda5, you will obviously need to change the root line. The last two lines with hash marks (#) may or may not be necessary, it varies from system to system. You might verify if the /boot/grub/core.img file exists in Ubuntu before trying this.