XST, does your new in-dash unit support Divx/MPEG 4 movies?
If so, you may be in luck. Most DVD players use a traditional DVD format which is proprietary and uses a special convention of known folders and file names for the various dvd elements, including the menu and the main movie. However, some of the newer players that support Divx allow a set of movies burned on a DVD data disc to play, just like some DVDs support a picture-viewer mode of CD-R's filled with JPG photo files. If your player supports this, just burn the files onto a DVD.
If your player doesn't support DIVX, then you need to consider your source material. Chances are the stuff you downloaded off the newsgroups is DIVX (or MPEG4) as that seems the codec of choice for peer-shared video on the Internet these days. If this is the case, then you will probably need a program that will transcode back to MPEG2, and properly build the necessary DVD menu files (the convention I discussed above...because if the player doesn't support DIVX chances are it won't support a data disc of MPEG2 files either).
Nero will let you burn a DVD from a set of individual movie files and it transcodes along the way and creates all the necessary menu files and such. I don't know if it can transcode DIVX files though. You will have to try it. Start with the latest version.
TJR