Many online retailers provide the option of purchasing a digital version of any movie in their catalog. Select the movie you want from a list of titles, choose your file format and complete your purchase. You will be prompted to download your movie to your hard drive, where it can be imported.
Blu-ray and DVD combo packs are commonplace items at most retailers, and many of them contain MPEG copies, as well. While the vast majority of these files will already be in the necessary format, you should double-check the packaging just in case.
If you already own a DVD copy of a movie but do not wish to pay for an MPEG version, you may use third-party software to create one. Be careful when selecting a product and download software only from trusted sites. Note that Title 17 of the U.S. Copyright Law states that you can produce copies of titles that you own only for your personal use.