This may not be the popular choice, since it's so expensive, but Nero 8 Ultra Edition -- if you can even manage to get the damn thing installed - has hands-down the best, easiest-to-use video-to-portable solution. It is a separate application called "Nero Convert". It does the BEST video conversation I have every seen, including Divx to mp4. With a good freeware video ripper, you can easily transfer your DVD library to your portable device. However, Nero Ultra is approximately $80 and a PAIN in the neck to install, and some have called it a resource hog. I love it, but YMMV.
IMtoo works well, and is less expensive than Nero, but harder to use than Nero Converter, and they nickel-and-dime you on the various components of the "IMtoo suite". IMtoo has had the market cornered on for-pay video conversion for some time. Freeware convertors don't quite offer all the functionality.
For a free solution, look into Videora converter. I haven't tried it with Zune (only iPod), but it IS free. The downside is, unlike Nero or IMtoo, it often requires a lot of research and calibration to get some videos to synchronize properly with the audio after conversion.
Good luck!