I have a Google Nexus One with Android 2.2. I didn't like the default SMS-application so I installed Handcent-SMS. Now when I get an SMS, I get notified twice. How can I fix this?

I would like to send text messages via Google Voice, as it is the number I give out for voice calls. However, I find sending SMS through the Voice app to be a bit cumbersome. The new widgets improve this somewhat, but it is still awkward. I would prefer something with an interface more like Handcent or ChompSMS. Are there any other apps that support sending SMS via Google Voice?