So here just to throw my experience into the mix...
Card: 5870E6
Driver: 10.6
Adaptor:
Bizlink Active DP to Dual-link DVI (dell resell them).
Adaptor Firmware: 034
Adaptor Model: BZL-KS10008(B)
For ages I tried to get this to work, without even any detection on my PC.
I have tried many combinations and port configurations, none of them worked.
I have however found a way to get it to work!!
Powering the device with a HTC phone charger that is a
240V Mains plug to USB 5V @ 1A, it works perfectly - not a single flicker!!!
I had previously tried USB1.0/2.0 @ 500mA even USB3.0 which provides 900mA to no avail.
Other USB chargers may also prove to help, such as those of the iPad which provides up to 1.2A.
EDIT:- I beleive that a custom built USB power cable would also work.
Method 1: Using 2 usb cables, split them both in half and solder the 2 male ends together linked to the female connector like in a Y cable splitter, this way you can use 2 USB ports to give a total of up to 5V @ 1Amp or 1.8Amp if using 2x USB3.0 sockets.
EDIT again or use this cable.
Method 2: Use a single USB cable, and attach the power cables to the 5V pins of a molex connector (+5v is RED with Ground as Black) that would normally be used to drive say hard drives/dvd drives, fans etc.
/EDIT
The cable connections are thus...
|DP>DVI(passive)| |DP>DVI(passive)| |DP>DVI(active)| |DP>VGA| |none| |none|
Each monitor running at 1920x1080.