I found an interesting article in a PC magazine the other day, which might help people who are building a PC or upgrading their PSU. I've come across this problem too while building my own machine.
What power requirements do my PC components need?
I've tried looking in manufacturers manuals and websites, but most fail to mention this vital piece of information. How do I know what PSU to buy? 200W, 300W or 350W, maybe I should go the whole hog and splash-out on a 400W Power Supply beast!
Use this rough guide to estimate the power consumption of your PC.
PC Component Requirements (Rough Guide)
Celeron - 60W
Pentium 4/Athlon - 70W
Fans (CPU/Case) - 10W
Motherboard - 60W
256MB RAM - 20W
512MB RAM - 35W
AGP video card - 30-80W
CD/DVD drive - 30W
Hard disk - 20W
Floppy disk - 8W
Sound card - 10W
Network card - 5W
Modem - 5W
Firewire card - 40 W
USB 2.0 card - 20 W
Maybe you should consider a cardboard case like the one below?
Sounds odd, but when you think about it there are many things that you could fit a PC inside. All you need is an ATX PSU (Power Supply Unit) and a switch off an old power supply (ATX style only), or you could make your own Switch/Reset using momentary switches from Maplin or the like.
Cardboard PC Case
Construct your own ATX PSU switch
If you fancy creating your own ATX switch and reset button, it's easy check out this site.
Apple Mac G4 PC Conversion
Maybe if you have an old G4 lying about you could convert the innards into a PC!