It's cool to see an SLI system with Semprons. Semprons are good overclockers. This makes them compete with high-end S939 system.
http://www.motherboards.org/articles/guides/1486_1.html
http://www.motherboards.org/articles/guides/1486_1.html
Low-cost and SLI don't go togather.
two cards are most assuredly better than one when run in an SLI configuration
Only "cheap" sli system worth even bothering with would be 754 Epox SLI board, 3000 athlon 2.0ghz, dual evga actively cooled overclocked 7600gs's.