seems to me you've already answerd the question. You love vegas and it's easy for you. So build the best Vegas machine you can. Vegas will take whatever CPU power you give it. Dual core, dual Xeon, Dual Opteron, then more the better. Thats aid it runs FANTASTIC on our DIY2 machine - which I use at home for all my editing. Vegas deosn;t require an expensive graphics card. Any off the shelf 128 meg card is more than enough.
Vegas does not use the RTX100 hardware. It doesn;t require any special hardware at all. If you want to get analog & DV footage check out the ADS Pyro AV Link Studio http://www.videoguys.com/pyroAVlink.html#api757 which includes Vegas+DVD and teh ADS Pyro AV Link converter.
1) I already have Vegas 6 + DVD Architect 3, so buying this bundle would be a waste of money. Do you know anywhere I could buy JUST the hardware?
2) Processors - what about the new AMD Athlon 64x2 4800+? It has out performed Intel on every bench test I've seen when it comes to video rendering. Would this be better or worse than a board with dual Xeon processors?