Compositing Nodes with Video Background?

I’m using 2.49.

I have a four second long video clip in the background, and I want to make the 3D object in the foreground blur. I figured I’d use nodes. I have never really used nodes before, but when I click on composite nodes and add an input and output, there are no render previews on the nodes. I added a blur node between the two, making sure all the parameters were correct, but when I render there is no effect. Any help is good, thanks.

To get a render out of the node compositor you need to select the “Do Composite” button in the render settings under the large Anim butt in the Anim panel.
In the node editor you can select the ‘Backdrop’ button and add an Output / Viewer node. Anything the viewer node is then connected to will show in the background.