you need a crossfire edition card. If ATI didn't change the requirement to have a crossfire card when they upgraded from the x1800 to the x1900 series, i doubt they will stop.
I posted the same link last time. Take some time to read it.
well i heard that the crossfire edition cards are just a way to get crossfire out there quicker to deal with nvidias SLI. eventually i think they will switch to two crossfire cards instead of just having one here look at these
looks like the GTOs can run without a cable or CS card with the newer drivers:
One of the hotty new ATI features is of course Crossfire. Crossfire normally allows you the ability (with the proper mainboard) to hook up another X1800 Crossfire edition (400 bucks) graphics card into your PC, which doubles up performance. BUT .. ATI recently released drivers (Catalyst 6.4 and newer) that make it possible to run for example two GTO's in one system with no need for a master card or that dreaded dongle cable.