Upgrades This Year

[x88x]

http://www.tigerdirect.com/applicati...050&CatId=3681 - CPU
http://www.newegg.com/Product/Produc...82E16813157226 - mobo
http://www.newegg.com/Product/Produc...82E16820220396 - ram

that would bring you to about $150

maybe this too
http://www.newegg.com/Product/Produc...82E16817371016 - PSU

but a little more for a newer GPU would go a long way too

I would say do something along these lines. Then add in a Radeon HD 48xx or 57xx or a GeForce 9800GTX+, 9800 GX2, GTX260, or GTS450, whatever you can find that will fit in your budget. Any of those cards will blow SLI'd 7600GT's to kingdom come.

I'm not very familiar with UK sources, but I think that should fit into your budget.

Oh, and btw, unless it's making your system overheat, the case is not making your system run slower. For that, I would recommend picking up a few system fans and utilizing some of those empty mounts.