Its mean mysql client must be installed on the qmail server first.
Well you have to have mysqlclient libraries installed to talk to another MySQL server anyway!
I have but still i am getting error. ERROR 2003: Can't connect to MySQL server on '192.168.0.64' (111)
So you have a basic connectivity problem:
1. Check MySQL is running on the remote server and is listening on that IP.
2. If it is, trying telnetting to port 3306 from the mail server to the MySQL server and see if you get connected.
3. Check you don't have a firewall running locally on both machines.
Etc etc etc.
-- Aj. Systems Administrator / Developer