Do a search on google for dvd rippers, it lists a load of shareware programs that you can use to turn short clips (5min) of dvd into mpeg that will run on powerpoint.
I used a couple of them for my own presentaions
I have played around with DVD shrink, and is over all quite simple to use.
Quality is good, and it is possible to just rip the bit of the film you want.
#however it is quite untidy, creating several files,, which if yourename the title, in my experience does not seem t o play afterwaqrds. EAch clip also generates 5 or 6 files, so storing into appropiate directories is essential.
For those who do not ahve a TV capture card, I would recomend it.
However, I will probably continue to use the capture card, slightly more difficult to set up, but only creates one file which is recognsed easily by windows media player, and does not require any further tampering, downloading of codec's etc.