Yeah, slices rule. To clarify, they are basically a portion of your picture that has been cut up. Let's say you've designed your whole web page's top banner portion in photoshop. Everything looks perfect, and you want to do some rollovers. Choose File>Jump to Imageready. Bam! Your image is now magically opened in Imageready. Now, there are different types of slices. You can cut your own slice, or, even handier, are layer-based slices. So, let's say that you have a menu that you want to change the look of the text on a rollover; each item on the menu is its own layer.
1. Go to the Layers palette, right click on the layer that has the text that you want for the rollover.
2. In the pop up menu, choose "Create layer-based slice" (or something close to that)
3. Now, use the slice selection tool to click on that area of the picture that has the text
4. Notice towards the bottom of the screen is the rollover palette for that slice
5. The rest is pretty easy- the tutorial has a good explination of how to get your rollover states.
The layer-based slice option in PS/IR is fantastic. When you are done with all your rollovers, right click on your layers in the layers palette and make an imagemap based on the layer so that your layers are links as well. Then save optimized. It will create an images folder for you and store the slices of your image in there. Then it will create an HTML page containing a borderless table that perfectly holds your sliced image together, pointing to the Images folder. It (imageready) will also write crispy clean javascript to handle the rollovers. Very handy for the beginning web programmer. Enjoy!!!