Curious, are you using the original DVD? I had the same issue of rebooting, but only when I had a
"copy" of the DVD in there. I like to keep the originals safe at home.
I used a HP brand disc first, and it would reboot if it was hot in the car and I hit a decent bump.
This happened every day, but stopped when I switched to a Verbatim brand disc. The HP disc
worked fine otherwise, but the hot temperature of the car must have altered the disc some how
(warpage, or dye). It never rebooted on the way to work, but on the way home it did. Texas heat in the summer!