I think what you mean is can you use the satnav screen in your car to display a PC output? The answer is that it depends. Probably, but you may need to hack into your wiring for the satnav screen and convert the VGA signal from the computer to either video or S-video or whatever you satnav screen uses to display its information.
The touch screen will not work with the PC unless you figure out how the current screen works, hack into the hardware and figure out how to share the controller of the touch screen with the PC and you satnav system. Then it will work.
After all of this time and effort, you will have the original satnav in your car and crappy looking car PC output. This is because the VGA standard for computer screens is much higher resolution than the video display of most average satnav systems.
The easier path is to remove your satnav screen and throw it away (or better yet, sell it and the satnav system on ebay to someone who needs a replacement), replace it with a VGA touchscreen and car PC and use iGuidance on the car PC as your nav system.