Dependant Pick List on a Web to Lead Form

I would like to have a dependant relationship between my Country pick list and State/Province pick list on our web forms?

E.g. client selects "Canada" they only see Canadian provinces and territories listed under "State / Province" pick list , client selects "United States" they will only see USA states in State/Province picklist.

Are there any templates HTML coding samples to see how to do this?