You are using a good free tool for decrypting your dvds. When DVDFab HD Decrypter puts them on the hard drive, they will be in dvd format (ie vob files). Most of the time you will not be able to burn these files straight to a recordable blank dvd—usually the files will be too large coming from a commercially made dvd and will not fit.
One solution for this is a program called DVDShrink. After you have decrypted the movie and have it on the hard drive you can use Shrink to reduce the size. Look for it here: www.mrbass.org and read the guides for its use. You could also use Nero Recode for this process, but you do have to decrypt the movie first.
Once it is the correct size, you could use Nero if you wish. Open Nero Burning Rom and select dvd. You’ll get a list of possible types of burns, select DVD-Video. Then import the files you got from Shrink, set your burning speed, make a label and burn to the disk.
Another option, the one I use, is to have DVDShrink output to an ISO file. It is an option you can choose within Shrink. It will compress the movie to the correct size and give you this image file. Then use ImgBurn to burn to a disk. Imgburn is a free burning program I find superior to Nero for most things, and especially for burning video. You can find it here: www.imgburn.com