How you described is how I'd do it, yeah.
As long as the card is installed well and plays nice with the motherboard, which it probably will, then Windows will boot well. It will not have a driver
so the card will show up as standard vga in device manager. Aero will be disabled.
Then you have to install the driver. I have no idea about PCI card drivers
from NVidia, so you should install from the CD that comes with it. Use Vista driver. Install manually if need be using the device manager.
If the driver installs well, you might have to choose an Aero theme in personalization to get Aero back.
Let us know how it goes and good luck.