I'd just go to any highstreet store, prices are all pretty much the same nowadays
When I hot mine the guy at Currys Digital said they made about £10 on a laptop as they have to compete with the lowest online proces. So you are as well to go there or PC world as anywhere else, at least you have somewhere to return it if there is a problem.
Any £350 - £400 Laptop will fulfill your needs so just go for a reputable make, Dell as _Tom_ says are good, Compaq, HP etc. Just don't be tempted to go for the real cheapies, the specs might be the same but the cases won't and buttons / keys etc don't seem to last very long.
AMD processors are usually a bit cheaper that the equivalent Intel and just as good so don't worry there.