I started writting this as a simple comment on the site, but it got so long, I have blogged the entry here.
Since your crash dumps show 2-3 different error codes - a different one each time, my 1st suspicion would be hardware - have you run the MS memory diagnostic tool on the system otherwise, check for recent driver updates.
If you need a 1hr course in debugging, have a look at http://uksbsguy.com/blogs/doverton/archive/2006/06/21/627.aspx. However we have not had a single instance of your large crash appear through our crash database - I checked, and the crash appears to be in a very well used and known piece of code, the classpnp.sys driver, which hales to NT4 for classic PNP support.
Failing that, time to call PSS. If you were to do nothing but run
kd -v -y SRV*d:\websymbols*http://msdl.microsoft.com/download/symbols -z memfile.dmp
on each dump you will see the different crash locations. Lots of different locations normally points to h/w or a rogue driver corrupting memory. Mark in his teched pres talks about how to turn on verifier to find these types of issues - from the presentation:
HKLM\System\CurrentControlSet\Control\Session Manager\Memory Management
LargePageMinimum REG_DWORD 0xFFFFFFFF
EnforceWriteProtection REG_DWORD 1
Reboot to take effect
Fri, Jun 23 2006 7:18 AM