It has taken me over a week!
Bought a lovely nVidia 650i Ultra board and packed it up to the hilt, including four gigs of pretty fast RAM (Team Elite 800) Windows XP (x86) installed perfectly, and very bloody fast, but after a few days I happened to notice that only 3.25 gig of RAM was recognised. Thought there was a problem until I found a couple of forum entries in faraway places referring to PAE mode and Memory Mapping or something else I'd never heard of.
Tried Vista (x86) same thing, only worse, only recognised 2.85 gig of the RAM.
Ended up installing XP x64
at least this sees ALL the 4 gig
Not happy as almost half the hardware (although totally new) was not recognised/no drivers for this platform.
Chewing the cud at the moment, deciding which path to take......
In the meantime
I found THIS LINK hidden well away in Micro$oftS vaults
The moral of this story is simply that if you want 4 gig and a useable system....
FORGET IT