The only two cards that support tri SLI are the 8800 Ultra cards and the 8800 GTX cards. The only motherboards that will support tri SLI are those based off of a 680i or 780i SLI chipset.
Honestly.. I would wait to spend that much money until the next generation of hardware comes along. The new 45nm line of CPUs and nVidia's 9xxx series cards. Most are speculating that two 9xxx series in SLI would destroy current benchmarks. So all in due time...
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XPS M1730,IntelCore2Duo T9300@2.5GHZ,2x8800MGTX in SLI,4GB DDR2 667 RAM,DUAL 250GB 7200 RPM,VISTA HP with SP1,17" with 1920x1200 resolution
Triple the investment for something that only pays off if the particular game is supported in the drivers?
For dual card configurations it might be worth the cost/benefit ratio, but I would have to have a hell of a lot of money to burn to invest in triple-card configurations...
