If I could make a sugestion since you want your dollar to go as far as possible. If your not completely set on AMD, you would be far more future proof with Intel. I have both a 939 X2 3800 and an AM2 X2 3800 system and upgrading is pretty limited as far as next generation upgrades. When quad AMD comes out, you will have to get a new MB and processor to upgrade (Ram too if you go with 939).
If you went with a good 775 Intel board and a cheap 805D dual processor to start with, you would only have to get a new processor to upgrade your system, and that includes the new Kentsfield Quad processor. This should give you at least 2 or 3 years of easy upgrading as you get the money up to do so.
I have enjoyed AMD for over 15 years but Intel has made a comeback by being very smart about it's new products. I'm not in anyway saying that an X2 3800 system would be bad, just that your dollars would be better spent on a currently better and smarter product.
My systems now do very well but I am 99% sure my next system will be Intel, it's a smart dollar spent right now. Good luck with your new system whatever it turns out to be. Compared to your current system, you will be very happy with the difference of your new rig.