Lloyd Alvarez has updated his BG Renderer script for After Effects CS3, and it now resides in its own panel, ready for use at any time. As I also just noticed, this new version seamlessly allows you to overlap processes; even if one render is already underway, another one will open, which was not the case by default with the previous script. You can get it from Lloyd’s site, which also includes a movie showing how to install and use it and a link to buy Lloyd a beer for his efforts.
This plug-in has been in heavy rotation at my studio, where it allows an artist to render in the background, locally, while continuing to work, and without the need for a copy of Nucleo Pro or the ability to set up a command-line render (which is what BG Renderer is actually doing for you). On a multiprocessor machine, if you un-check Use Multiprocessing and leave the priority Low, you can render in the background, gradually, and continue to work. Or you can crank it up to full render power, damn the consequences.
As Michael Bay would say, “Awesome!”