Decide whether you would prefer to rent or own the movie.
Sign up for a service such as Netflix. You can then order the movie online, and it will arrive in about one business day. You will have it for an unlimited rental period. Netflix only offers movies on DVD and Blu-ray.
Chose the video format. DVDs are the easiest video format to find online, but you can also find classic movies on VHS, LaserDisc and Blu-ray. Another option is 16 mm or 8 mm film. Not all films made the transition from VHS to DVD, or from 8mm to VHS for that matter, so do a quick Google search to see if the film exists in any of these formats.
Purchase the movie from online retailers such as Amazon, DeepDiscount.com or Buy.com. You can do a price comparison for the movie via Google Shopping to find the cheapest option for purchasing the movie. Another option is to search a specialized movie retailer website, such as MoviesUnlimited.com.
Search auction sites such as eBay and its sister site half.com when you are unable to find out-of-print movies.
Watch the movie via streaming video on YouTube, Hulu or at ClassicMovieTime.com