I used the memtest that comes with the OPENSuse 11.2 installation CD I also installed memtest to my grub boot menu. Seems like memtest doesn't find any memory at all?! But linux boots fine and recognized the whole memory amount. I already did some benchmarks and they finished without any problems.
Your problem sounds very similar to the one I had.
Memtest looks to see if you have LinuxBIOS tables, but doesn't support tables in high memory, so it fails. Since you are using SeaBIOS, you'd prefer that it used the BIOS tables. I modified SeaBIOS to destroy the marker for the LinuxBIOS tables after reading them (since they are no longer useful.) It's a hack, but it's quick and easy.
Suggestions: Use a similar hack to destroy the signature so Memtest doesn't get confused Use a version of Memtest that already supports high tables.
Thanks, Myles