By David Rosenthal.Photoshop CS2 has a very handy tool that many don't know about. It's the Image Processor, and it can be found in File>Scripts>Image Processor.
As you can see, it offers you several options, and nothing's easier for converting image types, resolutions, colorspaces, or running actions.
In this case I am batch changing the JPEG quality to 5 and resizing to 400x267.
When you click on Select Folder a standard dialog comes up. You can only select folders of images in this box, not individual files.
I chose to have it save the files in the same location. In this case the Image Processor made a new folder "JPEG" and put all the copies of the images in there. Now they're all JPEG5 and 400x267.