How to use rollovers to make subsets

[Graphixguy]

I'm trying to design buttons that show subsets when you rollover them. I can create a rollover for the button so that when you touch it, my subset appears. My problem is, however, that I can't figure out how to make the subset stay there so you can choose one of the options after you've moved your mouse from the original button. I've tried creating a new rollover for the subset itself, but then, of course, it appears when you touch it without rolling over the original button. Does this have anything to do with linking slices--? I'm stuck. (Using Photoshop 6 and ImageReady 3)
Thanks for taking the time to read this. Any help will be greatly appreciated.