I went to PC World to buy my desktop PC and paid about £1200 it was a very high spec. and it saved me making my own and all the difficulties of compatibility.
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I was going to go for a laptop but the thought of a laptop on my lap for hours on end put me off.
My Spec: 400GB HD (7200RPM SATA), 1gb RAM, Processor 3.4Ghz, 256mb Graphics (ATI) card reader, built in wireless, network card, modem, firewire port, wireless keyboard and mouse, TV output - all the inputs and outputs I'll need for a few years, 19" LCD etc etc.