Your not English are you? I have tried the custom vibrate on my phone and I think it only works with a custom ringtone or ringtones that doesn't have it's own vibration pattern inserted on it. I think some built in ringtones comes with it's own vibration pattern so it doesn't allow you to use a custom one. I am checking now for you.
In the mean time I have just found an awesome website for ringtones.
http://www.free-ringtones.cc