hi
consider using RMI, see this example for more details.
http://yama-linux.cc.kagoshima-u.ac.jp/~yamanoue/researches/java/rmi-ex2/
Also why not updating ur application to handle multiple users?
As for the threads you will need 2, and no need for yield the system will handle them.
if you like send me your code once done and i will check it for you.
mail me on
omar.bilani@gmail.com for more info.
good luck