Your original question was about how to raise a messagebox alert on the client, wasn't it?
Anyway, if you have a VB
function that runs on the server, you would call the function from the OnClick event instead of the OnClientClick event. Just like you have probably done a thousand times. That is pretty much the basic functionality of a button.
Umm. maybe you could tell us what you are trying to do, and we could point you in the right direction?