and yes - PSU and RAM
the UT SLI-D vs SLI-DR difference is only the Sil3114 onboard raid chip - which is good, since some have complained.
I like the upgrade path youleft yourself though
even if you get the 3000+ venice (and it is a good o/cer) - and you get sick of it - or it's limiting, you can eBay it and up the CPU to a 3700+ or even an X2
plus, if you eventually get there - the 7800GT or GTX's in SLI should be sweet
the 6600's and even 6800 Ultras in SLI - just barely come close to 1 7800GTX - so save on power and heat by using 1 card if possible....hence the eVGA 7800gt recommendation - and eVGA has a great reputation - and if I'm not mistaken they may now even be offering a lifetime warranty like BFG had, though I could be wrong
I was thinking you could hock the eVGA mobo on eBay or somewhere for 75-90 perhaps, if you went with the combo deal at the egg - this way - you're just about halfway to a maxed SLI config...(you'd have a DFi + eVGA 7800gt + A64)
but your plan seems sound either way - but just make sure the PSU can handle it