At the current (about £10) price of CloD, the thing to do is buy it, then sort out what needs fixing, not the other way around.
I don't tend to overclock, personally, but if you overclocked your CPU you'd probably get within range of the specs.
How have you only got 3.25 GB usable with a 64 bit OS?
Beside which, the difference between 3.25 and 4 in percentage terms is fairly small, and Windows will be taking a variable amount.
If you needed to go beyond 4 GB there were motherboards available that did that, one I bought to reuse a Core 2 Quad is back on amazon after being gone for a while:
http://www.amazon.co.uk/MSI-Intel-2x...therboard+ddr3
Careful, that board needs old style DDR3, 1.65 volts not 1.5 and even then it's a bit fussy, but it will take 8 GB. You'd probably need a new CPU cooler too if you changed motherboards, but even so, it should be a little over £100 total.
Then you would need to think about the graphics card, but if you've tried CloD you'll have a better idea whether the performance you have is something you can live with or you need to upgrade.