Advice on New System Build ~ $700 budget - maybe more

I need some advice on a new build primarily for gaming.

I currently have a budget of about $700, however by the end of this year that could increase to $900-$1000. I'd like to be able to start building now, but if it makes more sense to wait, I can do that.

I plan on upgrading this machine in the future as it's needed. I've been dealing with a Dell Dimension 8100 since 2001, and have upgraded/o-clocked/done everything to it - up to decent playability on high settings, etc. HL2 and Fear, but Crysis and newer games our now out of reach.

SO:

What's the best gaming build I can do for $700? Would I gain anything by waiting a few months until I'm at $900-$1000? Would I be able to at least build a decent upgradeable machine for $700 and then "finish it off" with another $200 or so at the end of the year?

I can use my current optical drives, and I'm willing to use my current hard drives as well if needed - so I really only need to worry about:

Processor - (at least a Q6600)
Mobo - (may SLI 2 cards in the future)
Memory - (I'm comfortable with limiting to 2gb now and adding more later)
Case - (I will be primarily air cooling)
Power Supply - (may SLI 2 cards - so I'm thinking at least a 500 or 600 watt?)
Vista (? - maybe? - for DX10)
Graphics Card - (geforce 9600? or 8800 gt? or other?)

Sorry this is such a rambling post. Can anyone help me?