Welcome, Newcomer. Crucial's scan tool is correct. Despite having 4 DIMM slots, each slot only supports up to 1GB. True, Win 7 x64 can support more than 4GB, but it can't change the limitations of your motherboard.
my theory is that if i upgrade my pc bit by bit, when it comes to a complete upgrade, i might be able to build on the cheap by using bits from my 531 that i've upgraded.
the main thing i'm aware of is that my mother board it behind the times, but i've never homebuilt a computer before and i've only ever changed RAM and graphics cards before so i'm a complete novice when it comes to anything else really.
here's the back of my pc, i think that it can fit a dualslot graphics card in, i'll open mine up tomorrow and take a photo to upload so you get a better picture. i've looked on a few links n i think it might be best for me to measure the dimensions of my current PSU too.
SO, if everything were to work out size wise, how much would my processor limit the usage of a decent graphics card like the hd5750?
also, considering I have 2x 1GB already in my pc, from what i understand a 2 x 2GB is preferable to a 4x 1GB setup. How cheaply could i obtain a 2 x 2GB setup? I'm reluctant to spend more than 40/50 quid on RAM.