It's unlikely that so many discs would be bad. The checksum error is pretty easy to get. All it takes is ONE byte (that's a 0 or 1) being read incorrectly for the checksum not to match.
BIOS is a good thing to update regardless. The RAM error is worrisome but the possibility also exists that the CD drive is dusty or otherwise impaired too.
I'd avoid OpenSuSE honestly. Once it goes unsupported (for a newer version) lots of problems come up.
You might want to try booting with
Knoppix. It's a live (bootable) distro that lets you test memory and hard disks. Also will boot from the CD into a graphical Linux environment. Ubuntu has a similar bootable disc but no harm in making sure it isn't a bug with it.