If you're driving on a paved surface that is in generally good repair, any laptop should do. Especially if it's in your lap, where your body will absorb a lot of the shock.
If you're driving down lots of gravel roads with the sort of washboard pattern of bumps in it, then even something like a "Toughbook" will likely suffer from a much higher rate of hard drive failure. It wouldn't be immediate, but over time you'd find hard drives had a much shorter lifespan.
What tends to work best though, is using something like Google Maps or MapQuest to print off directions before you even start. Something you can quickly glance at, unlike a laptop based GPS, which would only be safe to use pulled over on the side of the road. You should probably pull over before looking at a printout as well, but so long as you're not in heavy traffic, it's not as likely to be a problem.
Can I use a "normal" laptop as a GPS while driving my car or do I need a Panasonic Toughbook to endure the vibrations and occasional bump without the hard drive failing ??