if you are a mac user. download mactheripper (its free) and you can rip sections by chapters (or the entire movie). then download mpeg streamclip (its free) and in it you can take the file you just ripped (which will be a .vob file) and export it to a format powerpoint can use (avi, quicktime etc). if you are a pc user im not sure what program you can get to rip it but mpeg streamclip has a pc version too
EDIT in mpeg streamclip you can set an in and out so if you just want a 30 second clip from the chapter you ripped thats fine