You'll find that a good quality 300w PSU (CoolerMaster for example) will provide better, more consistant power than a cheaper 450w PSU.
I have a CoolerMaster 300w PSU that is powering a 3Ghz Athlon, 1.25Gb of DDR ram across 3 DIMMS, a Creative soundcard, 1 LG DVD-Ram drive, an MSI DVD/CDRW combo, 160Gb Hitachi HDD, 80Gb Maxtor HDD and a Sapphire 256Gb Radeon 9550 VGA card with no apparent problems.
I haave gone with a Hiper 350W PSU - the same as the one I have in my current machine - which runs pretty quietly.
Ordered it all from Novatech even though I could get a few cheapers bits and pieces elsewhere. Past experience of Novatech customer care and support has been excellent so I don't mind spending the extra few pounds.
Added to the above a WD 160GB hard drive and an FX5200 graphics card (I'm not into games!) as well as 1Gb RAM.
All told coming in at a little over £400 - I have a couple of spare optical drives which will go into it and I think it is a pretty good deal.
My friend should be happy - I've been promising for a while!