If you want to cut out a part at the beguining or at the end, you can select a "start" and "end" point in DVD2AVI before making the .d2v
If you need to cut more than one part, or part that is in the middle of the movie, you can use the "range selection" feature of TMPGENC (settings -> advanced).
But if you need to do a file size prediction, you should first find the starting frame and end frame fo the point you want to cut with vdubmod or tmpgenc preview and add this line at the end of your avs script :
(let say you want to cut part from frame 1000 to frame 2000)
Code:
Trim(1,999).Trim(2001,0)