a PSU gives out 3 Voltage lines - 12V, 5V, and 3.3V.
when the total W of power demanded from the PSU reaches a certain level (this applies to ALL PSUs) it will start being unable to supply enough voltage on one or many of these lines. If any of them drop too low, your PC will crash or turn off. some cheaper PSUs will claim '350W' but will actually stop delivering at, say, 270W instead.
Check out <A HREF="http://www.tomshardware.com/howto/20021021/index.html" target="_new">This Review by toms</A> to see just how bad some cheap PSUs can be.
I'm not saying the one you've picked there will be dodgy, just that it might. If you want to, you can pick up a separate PSU and an empty case, to be sure.
Antec and Enermax come highly recommended by Everyone (I have an Enermax 430W myself), but they aren't cheap. I believe 'Fortron' are a great deal cheaper, and also very good (recommended by <font color=blue>Crashman</font color=blue> frequently, I think, but I've never looked into them myself.)
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Hey - Just had a look at their website. They have some pretty cool cases there. I love the clear acrylic one halfway down! I'll have to get one...
I didn't realise you were based in the U.K. (I assume you are as all their prices are UKP) If so, Q-tec PSUs (available here at <A HREF="http://www.komplett.co.uk/k/ki.asp?action=info&p=35465&t=186&l=1&AvdID=1&CatID=13&GrpID=999&s=pl" target="_new">komplett.co.uk</A>) are quite reasonable - I recently used one to build a PC for a friend, and It's running fine so far.
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$hit Happens. I just wish it would happen to someone else for a change.<P ID="edit"><FONT SIZE=-1><EM>Edited by ChipDeath on 07/18/03 05:33 PM.</EM></FONT></P>