The DF-02 and the DF-03 chassis are completely different. The DF-02 uses a traditional battery pack to one side with the motor and electronic on the other side layout that is commonly found on 4wd Touring Cars.
The DF-03 is a radical new design which has a 2wd-esque layout in a 4wd package. Doing so presented some challenge, such as the center driveshaft going diagnol across and the steering assembly being way in the back.
It also has a rear transmission like a mid-motor 2wd.
The DF-03 IMO is a better choice then the DF-02. Consider it just from obsolescence point of view (DF-02 is on its way out from production).
Just use images.google.com and do a search and compare and contrast it for yourself, you'll see there's a whole world of difference.
If you do decide on a DF-03, come join me and other DF-03 owners in our thread:
Tamiya DF-03 type
There's a whole world of 4wd 1/10th buggies, you should do some research first, such as what your local guys are running and also what parts are available at your local hobby store before getting into this buggy. Some of the guys on the DF-03 thread has local shops that support the DF-03 buggies, most of us don't (mail order all the time)...