Have used MEMTEST86+ v/4.20 with the good(!) outcome that my 6Gb RAM is OK. Not a single flaw. I have not opened the case, however. Only tested all 6Gb in situ with MEMTEST booted from CD. Think I'll wait with the single memory bank testing until other options have been examinated.
I'm still thinking the hardware itself is OK and that I (we) maybe should be looking for a logical flaw somewhere. It seems to me, that in spite of Vista in Task manager reports all 6Gb as being present, and in spite of my Vista being a 64 bit version, it behaves like it's operating in 32 bit mode only.
Is there any place I can see or change the way Vista controls 32 bit or 64 bit mode?
Looking fwd to your ideas.