To begin with, create a seamless pattern in Photoshop. There are several ways to do this.
You can download a seamless pattern, and tile it. Check http://www.autofx.com for several free textures in their Download Software area.
Use the Patternmaker command.
Use Offset and Clone to create a seamless pattern.
Learn more about these techniques in CMP's Photoshop for Nonlinear Editors .
For quick seamless motion of any seamless background try the Offset Effect!
Select a layer, and choose Effect>Distort>Offset.
Animate the Shift Center on the X and/or Y axis.