While Front Row's integration with iTunes and iPhoto provides a nice, seamless experience, there are times when your needs demand a not-so-integrated approach -- say, for example, if you have an external hard drive full of videos that you'd like to watch on Front Row, but don't necessarily want to import into iTunes or copy into your Movies.
One solution to this is to create an alias that points to said external hard drive or any other folder on your computer or network. For new PC-to-Mac converts, an alias is the equivalent of a "shortcut" on Windows. To create an alias, right-click on the file or folder (in our case, folder) and select "Make Alias." Now, place said alias in the your Movies folder, which is located in /Users/username/Movies.
Now, you'll be able to browse and play movies of the folder that the alias points to. And if QuickTime can play the file, then so too can Front Row.