Hi Doc, welcome aboard. [excited]
SilvrWolf is right... it's just your basic slice job, and the use of altered copies of all the buttons for a simple 'rollOver' effect. However... you can do the whole job using just ImageReady if you like. Your specific image will definately be a fair bit'o work, i'll say that right off. 
This is a 'simple' effect to create in theory, but can be a long process to explain. In general, as mentioned, you'd drag Guidelines from your rulers into positions whereby all of the buttons are surrounded by Guidelines -- your basic grid setup. Then within ImageReady under the SLICE menu, you'd choose "Create Slices from Guides". That will automatically slice all of the buttons for you -- but no physical harm is actually done to your source image. They're just 'virtual' slices
You would then need to double-click on these slices (on their blue tabs upper left corner) and name them, plus fill-in a few other attributes for them.
And last... you'd need to assign the altered duplicates of all the buttons to function as the rollOver images.
And that's the basic gist of the method.
Here is a page where you'll find lots of info/tutorials on this:
http://www.graphicssoft.about.com/cs/imagereadytips/
Hope that helps.
And please feel free to aks for help with anything more on this. It can be a confusing effect to do if you're not used to using IR.
