Ok. I take it then you have ripped the movie from the DVD and now have an .avi with DTS audio. You need to demux the audio with VirtualDub, decode to 6 mono wav files with Tranzcode+TranzGUI and then load the 6 mono wavs into a AC3 audio encoder (such as Sonic Audio Transcoder - part of Sonic Scenarist - or TheAC3Machine if you want a free option).

Please stop crossposting. You may be new but I think you know well that your question doesn't belong in the "Bargain Basement" forum section.