For me whenever I've disabled Crossfire, the second GPU always receive a "Core Client Communications Error 0xFFFFFFFFFFFF" unless I had a secondary monitor connection and/or dummy plug connected. This was the case with all Windows O/Ses not just Win7/Vista.
But the part about -gpu 0 and -gpu 1 is correct and required. I don't believe the client can spread the load over both GPUs, though I haven't tried dual-GPU ATI folding in some time.
Shredder there is a measure of instability in the console ATI client. I've had the same thing happen with ATI clients in the past using this "dos box" version, where I hit CTRL-C, received some sort of popup box with an error, and all of the WU was lost. Not fun.
Better to use the SysTray client with the proper parameters set (ie. -gpu 0 and -gpu 1) and just pause it when you want to stop it.
You may also want to check out this Folding Forum post regarding environment variables that need to be entered to reduce physical CPU Core usage.
Folding Forum • View topic - ATI v1.24 Core available
Also, make sure to rename the AMDCALxx.dll or ATICALxx.dll files in the Folding Clients working directory to use the latest CAL drivers in the ATI Catalyst driver set, vs. the outdated ones with the folding client.