Definitely rent a car and try to drive around the area where you think you might be living at rush hour. Ask your wife to pick a few choice schools and see what the drive around them is like. Fairfax is a pretty big county, and keep in mind that it generally takes less time to drive outward (away from D.C.) than the opposite direction.

If your wife teaches at the high school level, she may be in better luck with regard to buses -- the middle and elementary schools are more numerous and spread out. An invaluable site for D.C.-area public transit users is www.wmata.com, which covers all the Metrobus/Metrorail routes serving Northern Virginia. You'll also want to check out the sites for the transit systems serving individual localities within Northern Virginia, such as Fairfax Connector, Alexandria's DASH, Fairfax City's CUE, etc.

I'm sure you'll be able to find a place to live that fills both your needs. Public transit in the D.C. suburbs can be hard to nail down, but it's definitely doable. Good luck!