yes its car powered: http://code.google.com/p/multidisplay/wiki/Powersupply
It's good that you're taking extreme voltage variations (such as load-dump situations) into account with your power supply design, but I suggest you still replace the 7805 with an automotive-rated equivalent part like the LM2940CT-5. It's a drop-in replacement for the 7805, only costs a little bit more, and is designed to withstand the nasty voltage spikes you find in a car electrical system. I discussed the design of Arduino voltage regulators for automotive applications in chapter 15 of Practical Arduino so that may be some help.
By the way, it looks a bit like Multidisplay is very similar to several existing projects so you may be able to get some inspiration from them.
GitHub - Magister54/opengauge: Automatically exported from code.google.com/p/opengauge
GitHub - Magister54/opengauge: Automatically exported from code.google.com/p/opengauge
MPGuino - EcoModder Forum Wiki
practicalarduino.com
Jon
Freetronics: www.freetronics.com