I have started a Paralax (I think I got the spelling wrong :) Scrolling Component over on CodePlex [http://www.codeplex.com/]. It is an open source type of project that is designed to help game writers create repeating scrolling backgrounds.
It is far from complete but has some basic functionality, such as a 2d Camera, Layer Oscilators and also Scrolling and Clipping.
If you are interested in either the code or helping me code it visi the XNAParalax Component http://www.codeplex.com/Wiki/View.aspx?ProjectName...
Or leave a comment, I would really love feedback.