If you're building a gaming system, I've heard A7M266 might not be exactly for you, since it only has one unshared interrupt. If you do consider going with DDR SDRAM, K7 Master seems to be a good alternative, or even K7T266 (just make sure you get the updated BIOS).
However, the problem with DDR mobos is that they're still raw and need to mature. I'm still waiting for a good DDR mobo to come out. If you're in a hurry, you might want to consider a normal SDRAM solution, be it Athlon or Pentium.
i would suggest the game theater xp from hercules over the sb live 5.1 and also the amd configuration you gave. i don't know about you, but i'm staying away from via chipsets for a while since they've been buggy recently. let them settle and stabilize first.