Check out http://newbcomputerbuild.com/
The build explained is all from newegg and may fit your requirements laid out here. The AMD 955 processor can def. be overclocked some more with the same heatsink. If your doing HD video you may want more HD space though
This project consists of compressed 640×480 video footage. These small video files were being eaten alive by the massive 1090T hexa-core processor and 8GB of RAM. Premiere Pro CS5′s increased performance with multi-core systems coupled with bleeding fast hardware will make fast work of any simple projects such as this, not giving the GPU enough work to really make a difference. These results do suggest that if you’re editing small-time video footage, you will not benefit much from using Mercury Playback.
So assuming u want to leverage MPE and since gaming is on the table
Tower @ $848 (ya i do up more small rigs/SFFs these days hehe) Am advocating single GPU set ups
Leaves you with $345.05 for a Graphics Card and Optical Drive. I didn't include them because of the new 6000 series being released and the optical drive is not relevant to overall system performance (just pickup the cheapest SATA one you can find).