Well....basicly U...a what the heck...
Minitutorial:
1. create a plane under Your model
2. create new object from create manu->dynamics object->madcar
3. this is the tricky part...what i did for these two cars was i attached all the elements of the car bode to one object and changed it's assign controller to madcar.
4.the continue of point tree is that i did the same for each wheel. so i simply attached the tire to the rim and changed it's assaign controller in motion menu to mad car.
5. after doing all that u should see how the elements of the car line up with that wire model of the car from Karba's plugin...but they will line up to the middle of it and u go to 6.
6. When u got here from 5...i couldn't resist myself

So for each element such as body and 4 wheels u gotta change their position in the mad car options.how to?simply, choose body for instance, go to motion menu and to assign controller, then enrool madcar and u'll see some options there, basicly names of the carparts that can be rigged with the plugin. co for the body u choose Chasis and right abofe those carparts there's a box with NONE sign...so as u can assume this is where u pick the madcar cause in case u wanna rig more than one car u can obviously use more madcars. so u click it and u choose the wireobject by deflaut named Object1.
7. all the steps from 6 gotta be done again for each wheel...however u should remember that u should mark left back wheel for instance, with the left back wheel of the madcar.
8. after done all that u choose the dummy of the madcar and set it where u want to start the animation. find in Modify Tab the Surface and choose your ground plane.
9. when u got ur madcar dummy checked u can see in modify tab many options. basicly u gotta adjust them all to fit with your model....sometimes it's a bit easier to scale down the model and the just adjust a bit the geometry size of the chasis and each wheel and axle length.
10. When u gat all that done just clik the update surface button in Modifytab couse i forgot about that and scrool down to find the On Run Driveing button. Hit it and have fun
Another animation from me...soon...still counting that somebody will join me for a bigger project. Hope that helps...

P.S. I can write a bigger one with some screenshots or sth but i think that anyone can do it if i done it with no help

But if i'm wrong then ask again, i'll try to help.