Button Fade Animation

I want to make a button that fades in on an over state and fades out when the user moves the mouse off of the button, I use alpha when I try to get this effect with other animations but I have yet to do it with a button.

How would I go about doing this, I don’t really have any knowledge of animating buttons besides the basic up, over down states. Thanks.

A lot of people have asked about this before so check out the this thread, it will answer you question. =)

http://www.kirupaforum.com/showthread.php?s=&threadid=5669&highlight=alpha+button