www.mgmaps.com.. Provided you can find a way to run Java midlets on your Car PC .
I guess its doable.. Just follow the instructions here -> http://www.mgmaps.com/winset/ . Except you may need to download "CLDC 1.1/MIDP 2.0 for Windows XP/X86".
I havent tried running mgmaps on my PC yet.. Will try it out today.