Virginia has no regulations concerning a GPS unit per se. (Some states do, such as California which does not allow mounting of a GPS unit at all!)

What you must be concerned with is an unobstructed view. In Virginia, you may not hang items off of the rear view mirror. (Rarely enforced... but don't press your luck.) Thus, place the GPS in a spot that will not obstruct your vision. I like placing mine to the top of the window, right of the rear view mirror. You may not be able to reach it there. If possible, maybe you should place it low and to the far left of the drivers column.

A second thing you should pay attention to is to not get distracted by the GPS! Secure it in place while parked. Enter the destination information while parked. Why? If you are in an accident and you state that you were "adjusting the GPS" (or talking on the phone, changing the radio station, etc.) you could be found at fault of the accident (even if the other person was primary) and also charged with Reckless Driving. (Example, my friend was properly in his lane when an oncoming truck crossed the double yellow line and their mirrors connected, breaking both off. He was on his cell phone at the time and told the officer so. He was not paying full attention to driving thus he was charged with Reckless Driving. Fortunately, he was able to plea it down in court.)

I can not seem to find the exact sections of the Virginia State Code online, and I am to lazy to go out to my car to grab my code book.

Good luck!