PC Specs help

[Guest CurtisAndroidSF2]

Basically, I currently own a Acer Aspire 5734z laptop, but it's no good for gaming so I'm looking to upgrade but I'm completely oblivious to the terminology of PC specifications so I'm lost. Here are my current specs;

OS- Windows 7 Home Premium SP1

Processor- Pentium® Dual-Core CPU T4500 @ 2.30GHz

RAM- 3gb

Video card- Mobile Intel® 4 Series Express Chipset Family (Pixel Shader version- 4.0, Vertex Shader version- 4.0, Dedicated Video RAM- 64 MB)

320gb hard-drive.

My current options are to upgrade my laptops video card (if possible) and upgrade my RAM to 4gb (My laptop will only support up to 4gb) or to buy a PC and use my 32" TV as a monitor. I'd rather buy a new PC if I can get a cheap enough deal (Under £300 would be perfect, the cheaper the better). I'd want to run a few higher-end games, even if its just on low quality, as long as it's playable I'll be happy. It'll probably be used to play games like Guild Wars 1+2, Diablo 3 (If possible), Starcraft II, Battlefield 3 etc.

Any ideas? What kind of specs on a PC should I look for? What graphic cards are useful for me and what ones aren't?

I'm also from the UK, and I'd prefer to buy in-store than to buy online as shipping is normally an expensive nightmare.

Thanks, I appreciate any help.