first guess, the /boot folder is not accessible to the grub bootloader.
Since you say that whether you boot “windows or openSUSE” it would appear you are getting to grub on the hdd mbr where you can select the partition, so if you can use the install dvd to access openSUSE, then you might be able to goto YAST->System->boot_loader and fix it from there.
Just a thought… I was having some issues with a drive lately after installing Suse 11.3 on a Desktop. I ended up in a similar situation. It seems that Suse wrote over my MBR and also wrote some files to the hard drive (NTFS) when installing and I ended up in a never ending GRUB circle. I was able to over come it using a system rescue CD from SystemRescueCd. There is an option on that CD to boot to a prior installation, which allowed me to get back to Suse. Once there, I was able to edit my GRUB “menu.lst” and restore my MBR. You may want to give that a shot.