Rule of Thumb for Power Supply Capacity?

[Calum]

Coolmax isn't a good brand, avoid them.
Scythe's 120mm fans are excellent, this isn't a machine that's going to throw off a lot of heat so I'd recommend the 1200rpm fans, quiet and still push a lot of air so you'll have lots of case cooling.

[computeruler]

Woops! I need to make a correction.  The grand total should begin with a 4 not a 2. 

[Calum]

Personally, I'd recommend changing a few of those parts recommended by computeruler.

CPU - cheaper, around the same performance.
Graphics card - more expensive but much faster.

If you don't plan on upgrading this system to use extremely high end graphics cards and CPUs, you'd be better going for a PSU around 4-500W and saving the $30 or so IMHO.