I recently did a web site for a client that involved chopping up a large image into about a dozen rollovers split into four sections that could be shown or hidden by clicking on the central image. Needless to say I spent about two whole days chopping up images over and over as they kept changing their mind about the design, not an experience I want to repeat in a hurry. Photoshop tries it's best to help with it's moveable guides, but if you want to subdivide any further it just gets so messy it's impossible to keep track of all the little pieces. If only I'd discovered SplitImage back then. It's a freeware Windows program that does all the hard work for you, outputs all the images as GIFs or JPGs and then generates beautifully clean HTML tables. It even lets you specify ALT and HREF attributes for the images. If you're ever faced with composite images, make sure you have this program.