Adding 2nd and 3rd Graphics Cards to EVGA 680i MB

I would like to purchase EVGA 8800 GTS 320MB Super Clocked VC as a starting point for a new gaming computer. I plan on upgrading CPU and VC and Water Cooling in the next 6 to 10 mo. as prices settle down and new products come out.

Current System Future System
Pentium D 805/w/free game $65. Quad Core - Unknown Specs/$$$?
Antec NEO 550 PSU 700 - 800 watt PSU
2 Seagate 320 GB 7200.10 - Raid 0 No Change
EVGA 680i MB 122-CK-NF68-TR No Change
Corsair XMS2 6400C4 800 - 2 GB No Change/Maybe Plus 2 GB
Lian-Li PC-7 Case No Change
XP PRO SP 2 Possibly Vista

My question is... has anyone had any success adding a 8800 GTX in non-sli configuration with a 8800 GTS (16x or 8x PCI-E slot)? What about 2 8800 GTX's SLI with a GTS in the 8x PCI-E slot? The 8800 GTS 320GB SC seems like a great value. If and when prices on the GTX's (substantially-$300-$400) drop, I'd like to still be able to use the GTX and GTS together. Thank You. constantine