I found an article on Microsofts web site click here which discusses the Physical Address Extension. To enable PAE mode, you have to add PAE to the boot entry in the BCD file. Open an elevated command prompt. Type Run BCDEDIT /SET PAE ForceEnable.
I am not sure what elevated command prompt is but I opened command prompt as an administrator and typed as above but 'run' was not recognised. I tried without 'run' and it was accpted but nothing seems to have changed.
It's a hard lesson to learn but it is not always possible to get a 32bit o/s to recognise 4GB RAM.
Because I now have 4x1GB cards all I can read is 3GB. If I take out 1GB I can still read 3GB RAM.
The apparent answer appears to be to reurn one of them and just keep three BUT if you don't have pairs of RAM in the slots the 'dual channel' technology is disabled and the RAM does not work efficiently. The actual answer is revert to 2GB of RAM or keep all 4GB RAM and get 3GB operating efficiently.
What am I going to do? I don't know yet but I'll tick the resolved box and worry about it for a few days!
The Asus boards (or some of them) seem to be able to manage the Dual Channel a little more effectively. In the manual for mine - the P5B-E Plus it says (in unfortunately complicatedese) that if you put a matched pair in one set of DIMM slots and a single stick in another (or for that matter a 512MB and a 1GB in one set of slots) the board will use Dual Channel for the memory it can, and use the overflow as single channel. Don't know how it does it, and TBH don't care much. It claims to do it, and I'll trust it isn't being a bad manual and lying to me.