Yesterday the new PCs arrrived. I sat mine up and left it yesterday evening copying my data to from the old to the new system. This morning I was greeted with a blue screen stating

Hardware malfunction

Contact your hardware vendor

And nothing more. After a reset I just get the BIOS prompts and then

Parity Check 2

The PC came with 2GB RAM and our IT guys added 2 more. I removed the 2 additional DIMMs and bootet. Voila. It worked. Placed the DIMMs back into their slots. Boots successfully. I hate non-reproducible problems

Next step was to boot from the Windows Vista DVD and starting the memory diagnostics. That's running at the moment.

[Update] The test came out with no errors. Now running it again, this time using the "Extended test"

[Update2] It's Monday morning, memtest ran over 60 hours without an error. I probably won't find out what the problem was, but for now the system seems stable enough to get rid of the old one.