in other words dont bother buying a crossfire mobo and PSU thats strong enough for crossfire and an additional video card for crossfire.
just buy a x1900 youll get real solid performance, with no extra variables.
trust me i made the same mistake, i bought a x1600xt, for $170 when they were newer.
now i spend an additional $30 on a crossfire mobo, and $30 on a PSU powerful enough for crossfire. if i buy an additional x1600xt to use in crossfire it would be about $128.
so total i spent ~$360 for performance somewhere inbetween an x1800xl and x1800xt.
a single x1800xt will outperform my two x1600xt. i can buy a saphire x1800xt for under $300 retail from newegg.
http://www.newegg.com/Product/Product.asp?Item=N82E16814102698
i would have saved myself $60, alot of hassle for finding crossfire specifications and required hardware, AND gotten better performance.
so, unless your like me and, already bought a crossfire mobo and PSU, dont do it...its in no way worth it.