1) i'd say try to see for sure if vibration and shock is the reason for the lock up, by leaving it on while the car is not running/ or driving multiple times. If it locks up then ur definitely not having vibration issue.
2) after that, i'd check whether the power supply is acting funny. Best way to do this is bring out a desktop psu + extension cable (if required) plugged it into the car and let it run. see if that locks up (make sure you take off the power sw cable from the car psu to the mobo, so it doesnt send any shutdown signal). If it doesnt lock up, chances are you got a bad psu.
3) next would be testing your software(ie winxp). Turn the system to safemode, drive around see if anything crashes. If you can not get the system to crash when ur in safe mode, you'll be pretty darn sure its a windows/driver problem. If that's the case, reinstall windows, don't install any driver or software after. drive and see if it'll ever crash, then add one by one by one. Or create a system restore for each install, and work backward to find which one causes the problem.
hope that helps.