If you're using Windows, you can download Winamp and extract the album art using it, but you'll need to use an image manipulation program (like photoshop or some freebie photo-resize utility) to change the image size and format. There may be other utilities though that can extract it without installing a full-blown media player, you could possibly search on Google for an album art extraction utility and see what comes up.
I don't know of any applications in Linux that extract album art, though I'm sure a few others do. You may be able to search on Google for those too.
I don't know for certain, but I do believe some Windows utilities for resizing will allow you to do batch resizing and renaming, and I'm sure that one could probably whip up a Linux script or terminal command that could rename many files all at once, if there aren't utilities that could do so.