I never had any problems with any kernel before 2.5.66 (beta or stable) 
locking up or crashing.
I activated the NMI watchdog and still have been getting some really 
massive lockups, but now I'm getting some crash dumps. Attached is a 
group of snippets from my /var/log/messages from a couple of bootups.

If any information is needed, just ask.

Regards,
David