I have a velocity micro with dual 4850 also. Crossfire worked fine in vista, but as soon as I upgraded to Win 7 the catalyst control center recognized one of the cards as "disabled adapter". Device manager recognizes both cards fine. Velocity micro has no useful suggestions and says its not their problem since I upgraded to Windows 7. There is a new BIOS for the MOBO but Velocity Micro won't even help me re-overclock it if I do that (System is factory OCed and "guranteed" by Velocity Micro - LOL). And there is no indication that upgrading the BIOS will fix the problem although it will for sure set back my overclocked system speed. Oh well. Probably won't get Velocity Micro again, especially a "guranteed" OCed system.
ATI's latest drivers (10.3) say they fix this problem. They lie.