hes running a celeron. dude you should just save up and buy a new pc if you want to play games. the best you are going to do with that is watch dvds (and it might still lag), i just built my boss a yumcha pc for $950AUD thats about $846USD or 517.706422 English pounds and it flies. 8GB DDR3 ram, 1TB hardrive, intel Q9550, asus motherboard, ATI 4890, cooler master case, antec 650watt PSU. it has everything you need. just shop around we got all this cheap, and you can play games for a good price. it shouldnt cost more than 35 En Pounds for them to build it for you. or you can build it yourself and save that. go to dell for that and they charge you 1100 pounds for that (more than double the price).
The only disadvantage you have buying all the pieces separately is the warranty- dell normally gives you one year. but if some company builds it for you (i dont know in the UK, but over here in Australia) they have a duty of care, so they have to find what is wrong with it and fix it (they are liable because they built it) - all the parts in a "yum-cha" built pc have around a 3 year warranty. they are just all individual. you have to know what is wrong and organise the warranty. (but if a pc shop builds it for you - they have to find out what's wrong and organise the warranty, its the law, The Aus legal system is based on the english one, so theoretically they should be very similar if not the same, bar new laws in parliament)