So in fact you need a bit more than just a motherboard...

Normally that's "General Hardware", but I'll answer your questions anyway...
Motherboard: EPoX EP-9NPA+Ultra or
MSI K8N Neo4 Platinum... Two boards that are very stable and have a lot of features ... They are very good, but cost less than your aforementioned $ 250...
Processor: AMD Opteron 165 OEM,
AMD Opteron 165 Retail or
AMD Athlon 64 X2 3800+ Retail... I know you're not going to overclock, but I would nonetheless suggest an Opteron... They have a larger cache than the X2 (video editing benefits from this), but run a tad slower... However, if you want it to be faster, overclocking (it's the cheapest way for extra performance) these is guaranteed to have better results than the X2's...
The reason for listing an OEM version (without cooler) is because I'd advise getting a better HSF than the standard one... This
AC Freezer 64 Pro is a lot quieter, and cools much better as well... So if you'd pick the Opteron, maybe get the OEM and buy this one with it...
Case: The case is somewhat personal... Some want it shiny, while others prefer a sober one... What's your taste like?
Power Supply: Enermax Liberty 500W or
Antec NeoHE 500W... They are expensive, but worth it... These are among the best power supplies available on the market... My favourite is the Enermax, but whichever one you pick, they're both absolutely great, having a modular cabling system (you plug in which cables you need), Active PFC, SLI "support" (certified powerful enough to power two graphics cards

) and a very high efficiency (which makes sure that nearly all of the power input is "used", so there is practically no loss of power, which would mean more heat)...
Memory: G.Skill 2x1GB DDR PC3200... No extreme low timings, but very good memory for its price... It will run in dual channel mode in your motherboard, providing higher memory bandwidth this way...
These are my recommendations...
BTW Welcome to you both!
