Should be a very solid gaming rig, The evga card is a good choice for a couple of reasons. First they are excellent cards, Also they have the "Step up" program, With the 78gt's hitting the market very soon it may be something to consider.
Processor: AMD Athlon 3800
Motherboard: Gigabyte GA-K8NXP-SLI nForce 4 SLI Audio/GB-LAN/PCI-E/USB/IEEE/SATA/DDR/ATX 64 939
Video Card: eVGA 6800 GT 256MB DDR3/PCI-E/TV-Out/Dual-DVI
Power Supply: Enermax EG565P-FMA REV.2.0 ATX 2.0 w/SLI Support 535W
Will these all work together to make a good machine? Or will different things be better together?