Here ya go:
The VIDEO_TS and AUDIO_TS must be within another folder, point IMGTool at that and it will create an ISO for you. Free.
BTW, if there is no AUDIO_TS, just make one (leave it empty!) in the parent folder. Never tried to use IMGTool with any extra folders such as you have, don't know how it'll like that, but give it a go. Also, when burning with DVDDecrypter, let it set the layer break automatically. Tools -> Settings -> ISO Write Mode -> Options -> Layer Break (for DL Media) -> Calculate Optimal. That's your best bet, some folks say that works fine, others no. But not many people so far have been willing to experiment. The trouble is the layer break, of course. When you do ISO Read -> ISO Write in DVDDecrypter, the layer break bit is preserved if you weren't silly enough to mess with the defaults. No other method I know of is reliable, unless you count the latest RecordNow. There's a thread on that over at Videohelp, blah, blah. So tell us how it went.