Power Supplies

350W is enough, you will never reach 300+ unless you would start overclocking your CPU to mad speeds or plug in countless of demanding devices which i'm sure you won't. But with the future in mind it would not hurt to get a 400W, but that's only if the DX10 generation gfx-cards will really get as insane in power usage as the rumors talk about.
The most important part of finding a good PSU is by looking at efficiency, I think they are around 80% or 90% now... I haven't upgraded my PC in a while so I can't really recommend you a good brand but most dudes go with Antec. High efficiency means the PSU will have a easier job at preventing power to get lost as heat. Because more power gets saved the actual power capacity is higher and in turn will also result in a cooler unit since there is less heat to be generated.

Jam it back in, in the dark.

it should usually be included in the description. but if that's not the case, your best bet is to google on the name + efficiency. you can also try visiting the website of the manufacturer or reading reviews. for the latter, i recommend this website since they are up to date with most things and review anything PC related.

hope it helps

Most amazing jew boots

Cool, that calculator is really handy! Thanks for the info

This thing is sticky, and I don't like it. I don't appreciate it.