I may be wrong but I believe you need to check with the card manufacturer to get the straight answer on this. The card may give you the dual monitor support you want or it may not; again, I believe it depends on the specs built into the card by the manufacturer. I do not believe all cards with a certain graphics chip such as the 6800xt can be assumed to have full dual monitor support (meaning you can display a different desktop and run separate apps on the two monitors).
If the card will not give you full dual monitor support, one option is to install a PCI video card for the seondary monitor. For running non-gaming apps, you could go with an inexpensive PCI card; no need to have a PCI video card with a high performing graphics chip for email, web browsing, etc.