As for the CDs not playing in your car -- some CD players are picky about what CDs they want to play. CDs that you burn at home and music CDs that you purchase in a store are very different -- CDs that you burn at home are actually "burned" -- a laser actually changes the chemical composition of the material on the CD, so certain areas are lighter than others in accordance with the binary data you're writing to the CD. CDs that are purchased in the store are different -- the material actually has "pits and valleys," much like a vinyl record. Either way, the end result is that the CD player laser reads differences in color/height and plays that back. Some CD players are more sensitive to the pits and valleys and "choke" when they encounter homemade CDs, which don't have the pits and valleys.
Another thing is to make sure that you've set iTunes preferences to make "Audio CDs," and not "MP3" or "data" CDs. If you are positive you're making "Audio CDs" with iTunes, it may just be that your car CD player is too sensitive to homemade CDs. It may also help to try a different brand of CD-R disk, as some are cheaper than others and don't yield as high-quality a burn as others. I would recommend Verbatim brand CD-Rs, as they seem to perform the best and have a long shelf life.