Rackmount audio editor/recording

Hey guys - I built an audio editing machine based around the q6600 a while back for a studio, and the guy liked it so much, he wants another, but this one is a bit different. It needs to go into a rackmount case. I know there are standard rack sizes for servers and such, but I don't know if they're the same size as the standard professional audio rackmount inside regular SKB cases and such. I'll get dimensions soon - but does anyone know off hand?

I've never built a rackmount system before, so I'm looking for a bit of aid here. Couple questions:

1. Will ATX/mATX motherboards fit in rackmounts? I'll probably use an mATX board, for the size, obviously.

2. Will standard ATX power supplies fit in rackmounts, or do I need a separate standard size?

3. Obviously, for use in editing and recording, the PC needs to be silent...and obviously, because of the low clearance of the chassis, I won't get nice big fans that are quiet. Can anyone recommend me a heatsink/fan that's quiet and cool, and will allow me overclock some?

4. Do rackmount cases and power supplies and such have a typical premium over consumer products? I'm thinking that, if so, it might be easier just to get a lower clearance PC chassis and mount it to a sheet of wood or steel.

I'm still mulling the actual PC parts over, I'll get a list up here sometime. Budget is ~$600, but preferred less.