pulling video off home video DVD

Hi All,
I have home videos that I've burned on DVD. I would like to make a dvd of "The Best Of". However when I load the DVD my Imac jumps right into IDVD and starts playing the dvd. How do stop this from happening and how do I get these movies into IMOVIE to make my new movie?

If these at basic questions I'm sorry but I'm a NOOB to the mac world.

thanks
Mike