Shoot. Hmm. Well, he just tried reinstalling 7.1 and the SCSI2SD partition got corrupted.
So this leads me to believe it's either bad RAM or bad SCSI. However, the client said the machine was a lot more stable after upgrading to 7.5 despite it not being able to turn on 32-bit memory addressing. It was, apparently, crash prone when in 7.1.1. So if it was more stable when only using 8MBs of addressable RAM. That sounds like a bad RAM chip to me.
I'm thinking that one of the RAM chips perhaps got damaged or josseled during shipping somehow. Not sure how, but somehow. That could explain it.