It sounds to me that you want to start with the button disabled, but then have it become enabled once:
a) both the password and the confirm-password edit texts have some text in them (perhaps >= 5 characters... weak security, but probably fine for this app.)
b) the texts match each other.
The key thing, then is to *listen* to the event of text changing in the EditText views, so you can respond to it. So you'll need to add a listener for that... e.g.: http://stackoverflow.com/questions/4310525/android-on-edittext-changed-listener