Re: Crashing when SMP enabled
I've seen the vesa driver spew this warning on systems as well, and there was no instability associated with it, so I believe its just a harmless warning (or perhaps a harmless vesa driver bug):
(WW) VESA(0): Bad V_BIOS checksum
If you only have one onboard NIC, and its running with forcedeth, then you don't have a Marvell NIC.
The fact that older kernels were stable, yet newer kernels are not could suggest a kernel bug, or perhaps a BIOS bug that gets triggered by changes in newer kernels' behavior/codepaths.
I'd definitely encourage you to get a serial console setup. That will provide a good starting point to debug the instability, regardless of its source.