Okay, here goes.
I assume you have 3 separate DVD's and you want to put all three onto 1 dvdr and with no loss of quality.
Run DVDDEcrypter, select IFO mode, then Stream Prosessing tab. Click on Stream prossessing and UN-Tick all the audio and subs you dont want. Highlight the fist Video stream and tick on Demux. Highlight the Audio stream your keeping and click on Demux. In Tools/Settings/Ifo Mode make sure "File Splitting" is set to None and that Chapter Info - Maestro is selected. No hit the big go button. Soon you will have 3 files, one big Video *.mp2 file, Audio *.AC3 and Chapters *.CHP Do this for each DVD and save to separate folders.
Read the DVD to DVDR tutorial to understand the running of Maestro. But we then click on Movie and select Make new movie, do this twice so now have Movie1, Movie2, Movie3. Double click on each to bring up their Timeline windows. Load all the *.mp2 and *.ac3 files in and then drag them to these 3 movies timelines. Add the chapters.
If you want a simple Menu, design one in your favourite Graphics Editor (I use Paint Shop Pro) Mafe a blank window 720x480 if the movies are NTSC and 720x576 if PAL Set it out to your liking but keep away from the edges as TV playback will cut these off. Then load this into Maestro, move to Menu1 timeline window, use the Mouse to put a sqaure around each of the 3 movie titles you put on the menu, rightclick each square and assocciate to the appropriat Movie. Go to Advanced and hit Auto Assign to set up you remote controll funtions
In Connections, you need to assign First Play, this shoud be Menu1 and also setup the End Action of the LAST chapter of each movie to also be Menu1. So when Movie 1 finishes , it jumps back to the Menu ready to select the next one or stop or whatever.
Now compile and burn. Again read the tutorial.
Hope thats enough and that I havent missed any critical point.