If your just going to upgrade later get a vanilla AMD A64 3000+ because its not worth the extra bucks probably(unless the price dif is next to nothing). However, if you can put off buying your system for a month or two then do so and get an core duo instead, they are cheaper and beat AMD's CPU's bang/buck. However as carl said there may be price reductions from AMD to counter intel, so who knows what will happen in that case, AMD may be able to level the price-performance ratio at the mid/lower end to beat intel there....
For a GPU i would get a 7900GT, sell it at a later date for a beasty DX10 card(and they are looking to be amazing i think). If thats too much a 7600GT(and make sure its GT, beats the GS) would do fine until DX10...
So without SLI if you still want S939 then get a different mobo, maybe an MSI or biostar, dunno but you can save $30-40 that way.
And get the PSU Reather suggested without your SLI. Sorted