Crossfire is the dual card configuration for AMD cards. SLI is the dual card configuration for Nvidia cards. Crossfire and SLI would have a HUGE effect on current games if you ever chose to buy another (460 or 6850) card. Granted your only playing Cities in Motion ATM, but later on the CF/SLI would be beneficial.
As for the solution to the problems, upgraded drivers fixes the issue. As you can see in the link I posted above. If you really aren't sure though, just get an Nvidia card.