Go to the market and download "Smart Vibrator". I have been using this for a LONG time. It allows you to set custom vibrations for SMS and/or phonecalls. For example, for SMS, turn off vibration on the SMS app settings, and enable it on the Smart Vibrator settings.
Operating the app is very easy to. You can use "." for short vibrations, "_" for long vibrations, and any combination of the two.