The 7300 series most definately supports a dualview setup. My only thought is that you may not have the required ForceWear driver for the 7300 series. you can pour over the specs here:
NVIDIA® GeForce® 7 Ser
and see if you find anything else of interest.
The current release for ForceWear is 158.24 for Vista (64-bit), which you can find here:
NVIDIA Drivers
Hope that helps