Re: nForce 4 corrupting data written to HDD
I reviewed the LKML thread that you referenced and the problem descriptions there sound vastly different from what you're reporting. Your issue sounds like filesystem and/or in-memory corruption, however the issue on LKML isn't occuring on the filesystem level, but in the files themselves.
Additionally, you stated that "it boots with some scary messages" and "mplayer segfaults". It sounds like the data on your disk(s) is getting corrupted even when its not being actively written to, which is not the same issue as was reported on LKML.
At this point, the information that you've provided suggests a hardware problem (faulty RAM or disk). If you can provide information that suggests otherwise, I can look into your issue further.
I'll look into the LKML issue, however the information that you've provided here is not the same as what was reported on the LKML.