Simple button problem

hello all

I’m a beginner in flash MX there’s something that I can’t do with buttons:

I have to do a aplication that needs 30 buttons, and I don´t know how to make the user know wich button he already seen, when he goes back to the frame where the 30 buttons are.

this is probably a very simple thing to do but I cant’t seem to do that.

Do I have to do something in the action script?

thanks
Gritante