If you are on XP, try Mpg2Cut2:
http://www.geocities.com/rocketjet4/ . If memory serves, you will then need a burning program that will convert/author the resulting mpegs to standard DVD format.
I've not had any luck getting it to work on Vista, and use VideoReDo which wasn't free (about �35) but is easy to use and does a great job of slicing out ad breaks etc. I use it to author the whole DVD; the only thing that I'd like to change would be the limited menu options.