You can use Milkshape3D, anim8tor, 3D Studio Max and so on.
Several file types are supported by DBPro. I model in Max to export out to .X
Once created, you will need to load, position, maybe rotate or scale.
goto www.gamedevvault.com/dbpro/race/race.zip and download the file. It is a small (yet very untuned) race game I made 2 weeks after I got DBPro.
It does not run very fast, even not at all on some computers because I did the SYNC wrong, but it does load .X files and place them on the game grid.
In addition, there is a full set of keyboard controls for your car in the game and an opponent driver you race against.
I would not build on it becasue it has so many flaws, but use it as a learning resource for the different parts it has in it.
hope that helps
Cypher