It's a little tough to come up with an answer when you didn't list your monitors (?!)
You should be able to run both monitors from one card (one off of the VGA port). I would ask ATI to be sure. This is probably too new of a question for everybody due to the infancy of our Motion forum.
The Radeon 9800 Pro Mac Edition will run a Digital (DVI) connection - preserving your monitor's USB hub, and an Analog (VGA) connection - which runs a lot of standard (even CRT) monitors.
Good Luck!
- Joe