On second install all of the issues with updated BIOS and memory timings worked out so no BSODs. I was also rebooting after each app was installed in order to isolate what caused this (and other) errors that came up in the first pass at installing Vista on this machine.
The error is:
Unsupported 16-Bit Application
The program or feature"\??\C:\Windows\Twunk_16.exe" cannot start or run due to incompatibility with 64-bit versions of Windows. Please contact the software vendor to ask if a 64-bit Windows compatible version is available.
It occurs during the (extended) user login (after entering password, while Vista applies all the user settings).
Sometimes it does not occur but most times it does (login after a logout, reboot or cold boot).
The first instance occurred after installing Adobe CS3 and Lightroom (I did not reboot between these installations but did reboot just before and just after).
Since the error does not always show up it is possible that something installed before CS3 and/or Lightroom caused the problem.
None of the Startup or HKLM/HKCU run items cause this (unless it is something like the Kernel and Hardware Abstraction Layer service) because it will occur when everything possible is removed from these places.
This is one of the last two issues that still exist for this new and rather spectacular computer build I put together over the last month.