Sprint HTC Hero :: How To Turn Off OEM Default Messaging Program?

I installed Handcent because of the battery drain issue, and like it a lot, but now I cannot turn off the OEM Messages program. I tried going into the Settings>Applications>Manage Applications to turn it off, and it doesn't work. I also did the "Use Handcent as default SMS" when that box first pops up. I get two different ringtone notifications too. Although I switched the ringer to the same one both through the phone's settings and through Handcent's settings.