Ripping is the process of removing the copy protection and copying the files to hard disk.
If you want to retain original quality then all you need to do is rip the discs and copy the files to the NAS.
Some people prefer storing disc images on their NAS as there's only one file per disc and you can store all your films in one folder but it's down to personal preference.
I'm not too familiar with HD DVD but if you want a program that rips and compresses all in one then I'd suggest you check out the trial version of DVDFab.
DVDFab will rip HD DVD and rip and compress Blu-ray but I'm not sure if it compresses HD DVD or not.
Try it though and see how you get on.
If you're prepared to do things in multiple stages with multiple programs though then there are plenty of other good programs to recommend.