I'm not sure what apps you're using for video editing, but I hear that Intel does better with video. Most of the adobe programs prefer Intel's with hyperthreading.
CHAINTECH "V915P" i915P Chipset Motherboard For Intel LGA 775 CPU -RETAIL $92
Intel LGA 775 Pentium 4 520 2.8 GHz, 800MHz FSB, 1MB L2 Cache, Hyper Threading Technology, PCI-Express - Retail $158
I'll second the GB of RAM that brad mentioned.
Hopefully you know more about video editing then I do. Maybe you could get away with onboard video since its mostly 2D stuff, right?
With the RAM mentioned above... that puts you at $285 before shipping. Really pricey.. Hopefully someone else will chime in. If you have spare things like a case, ps, optical drives, that'll save you some $.
I recommend a SATA drive for this stuff too.