i would mostly be using the internet, playing online games and gaming, so it does not have to be very good, but good enough to last a few years without being too outdated. What would i be best spending my money on?
I'm afraid that I'm going to have to disagree with your original assumption. For gaming, you are going to need an almost state of the art machine. I don't know how far GBP 400 will go, but my general advice would be:
1. Buy a desktop machine, not any kind of portable. You'll be paying about 1/2 price for the same capabilities.
2. Talk to a local computer shop about buying a Brand X using medium-grade components, not a brand name like a Dell, Lenovo, or whatever. When buying a name brand you're paying for OEM support which is worthless anyway. I've had only good experiences buying mid-range hardware, especially mid-range motherboards.
3. I would buy a motherboard with an Intel chipset, even if it's more expensive. If you can still find one, buy a 32-bit system. You should also buy a very good video card. Buy Windows 7 - I can't tell you which version from personal experience because I have some security manias, but a professional techie I trust claims that home edition is good enough for most people.
4. You can skimp on a cheapie sound card and speakers and the DVD burner. (Don't buy any fancier kind of optical media drive.) Don't buy a floppy drive at all. If you can stand it, buy a CRT monitor instead of anything more modern. It will be much cheaper.
My 2 cents. (= about 1p)