Anyone know of a way to run multiple clients on netbeans for a java program, i need to test my server which takes in x amount of clients. Currently i can only run 1 client with my computers hostname and the server but cannot test if the server will work fine if other clients connect to it.

You could create a simple small test driver that starts multiple instances of the client, passing different values for host name, port number or whatever else can't be shared with its default value by two clients on the same meachine.

Or just run the clients outside of Netbeans...

yes, but in that case he will need another way to input whatever values need to be unique for each instance, and will lose access to Netbeans' debugging tools...

he'll need those anyway to deploy his thing after it's complete :)
And he can run one inside netbeans for debugging, or attach netbeans to one of them using the JVM remote debugging system.