That is really strange that the text I quoted just appeared in your post without you typing it, I have never seen that happen before.
I am sorry, but I have no idea how to solve the problem you are having. The available email programs should just appear in the drop down list where you are trying to change it from and you would just select the one you want to use. Since Yahoo, as far as I know, is not an actual email program, but rather webbased email, I do not know how you would get it in there. There must be a way though, and someone will probably be a long soon with some ideas.
Btw, welcome to BleepingComputer
Edited by Stang777, 14 October 2009 - 07:21 PM.