1) good budget you can do better for that cash
2)Why the choice of MoBo - you are buying a Mobo with built in Graphics and then buying more graphics. Dont bother with the built in graphics. Try this
3)Graphics. Unless you are playing at over 1600 resolution (check your montior maximum, and your tastes), no need for the 640Mb version. get the 320 Mb version
4) you dont need 4 GB RAM for gaming. Get 2GB of PC2 6400 (800Mhz). If you aren't planning on overclocking, choice isn't critical.
5) PSU- ARG!! I don't know anything about that brand, but 600W PSU for £20 scream AAAAARRRRG at me. possibly followed by the smell of burning electrics and pound signs floating away on wings. Don't scrimp on this!!! buy something like one of these
6)No overclocking (a bit of a waste) = no need for aftermarket heatsink and fan
I'm sure others will give better advice. Try the tutoral sticky at the top, it has some recommended builds
EDIT: Ahh... My bad, the link for you mobo on aria has a description of a graphics card, hence I though it was a mobo with built in graphics. I know nothing about your mobo. All the same, the link I gave you is really good.