Alright, I've given this some more thought this morning. After some more research I think I might be able to successfully build my own computer. And doing so does seem to have its advantages: I can find individual components at their best prices and also get different parts that websites might not stock.
But, since this opens up a whole new level of customisation, I have some more questions if anyone can answer them:
a) I'm still intending to get the Intel Core 2 Quad Q9450 Processor, but are there certain motherboards / RAM that go better with that than others. Or are all of them above a certain price level going to perform adequately with it?
b) With research it seems as though most of the components that I'd order I just make sure they're compatible and fit them together. But with the processor it seems that I'd not only have to order the processor itself, but also order and fit to it a heatsink and a fan. Is that true, and how easy is it to find the right heatsink and fan and fit them? I mean, I'd rather not have to do this, but the "retail" versions that come with a fan are apparently so shite I'd have to take the fan off and replace it anyway?
c) Should I go with DDR2 RAM and motherboard, or DDR3 RAM and motherboard? DDR3 seems to be a lot more expensive but I've also heard it's much better from some places. Others still seem to think it's much the same, though.
I'm sure I'll have more questions when I get to them.
Thanks for all the help guys.