JonathanDeane didn't mean burn them at 2X speed, he meant that you shouldn't burn them at MAX speed. I would burn your movies at a moderate speed.
It can also depend the brand of discs your're using. Expect more coasters with cheaper or generic brands especially if your burning at MAX speeds. Also, as noted, you might want to update the firmware of your drive. If the link provided doesn't have your EXACT model, you should be able to obtain it through LiteOn's website. In the past, FireFox didn't seem to like downloading from them (probably a problem at my end), but I.E. works.
Do not use images. RIP your DVD directly to your hard drive in the DVD folder (TS_Audio & TS_Video) format. Then use Nero to burn them from the hard drive to disc. Do not use the DATA DISC method. Nero should have a method to specifically burn DVD Files from your hard drive to a blank disc.
Also, while in Nero, click on the "More" button right before you burn the disc. There are several options you can apply. Unfortunately I cannot remember them exactly, but one will supposedly allow for better readability in stand alone DVD players. It might work for you.