You can go through and manually check-out all data sub-folders except cars and tracks, and then check out only the cars and tracks you're interested in... but that's not a good long-term solution. I think to really make this work we'd have to restructure the svn data tree to only have maybe one car and one track, and then put the rest of the cars and tracks in a separate location in the data repository.
I'll make an issue about it:
http://code.google.com/p/vdrift/issues/detail?id=133