Get designing ... design both of the states (the normal+over one),in separate layers that are easy to hide, or just have a Colour Overlay effect for that layer. Slice it .
Click the Jump to ImageReady button on your toolbar (Ctrl+Shift+m) .
Get the slice select tool. Click on the desired slice . You will notice a Slices palette in one of the windows . Click the 'Create rollover state' button,in the ROLLOVERS window.
Now,with the rollover state highlited in the Rollovers window,go to the LAYERS window and make the layer/effect ( the one that makes the rollover effect) visible .
Click back on the Normal state in the ROLLOVERS window .
Repeat for each slice .
Then go to File>Save optimised as.I think you know what to do from here .
