Avic D1 and D2 Comparison

I'm looking for a basic navigation system that is affordable. I don't see too much of a difference between the Avic D1 and the Avic D2, besides the price. I understand that the DVD drive is only a DVD-ROM and will not play DVD movies. Is there anyway to convert the DVD movies into a different format and then play them on the DVD-ROM? Also, is there a chance that the vehicle motion bypass will not work? I've located several websites with instructions on performing the bypass, but have also read several posts on installers unable to get the bypass to function properly. If I can find a good deal on the Avic D1, am I going to be dissapointed that I didn't get the Avic D2? Lastly, am I connecting the VSS wire or not? I've read posts advising that you should not connect it in order to get the motion bypass to work properly. Will the accuracy of the GPS be altered because of the bypass?