Nope, not at all! 
Around these parts: the only stupid question is the one that doesn't get asked!
Have you installed the drivers for the Sonnet G3 Card?
Have you determined that it is working correctly?
By "works," do you mean that you can choose amongst all "availabe" resolutions from the VidCard or that it gives you 640 x 480 just fine without even loading the drivers for it?
Does the Computer boot:
When either card is installed alone and both of the card's drivers are correctly installed and activated at the same time under the "Extensions Manager" Control Panel?
Around these parts: the only stupid question is the one that doesn't get asked!
Have you installed the drivers for the Sonnet G3 Card?
Have you determined that it is working correctly?
By "works," do you mean that you can choose amongst all "availabe" resolutions from the VidCard or that it gives you 640 x 480 just fine without even loading the drivers for it?
Does the Computer boot:
When either card is installed alone and both of the card's drivers are correctly installed and activated at the same time under the "Extensions Manager" Control Panel?