more infos at http://mamoworld.com/tutorials/relative-file-path-nuke
In this tutorial you learn how to use Relative File Path for NUKE.
Sometimes you just have to move your project files to another hard drive and relinking your footage in NUKE is not a pleasant thing to do. But if you use Relative File Path you won´t have to worry about that anymore. Because after you have applied Relative File Path to your NUKE script you can take the folder that contains all the files of your NUKE project and move it anywhere else without breaking your footage links.