how to cirvumvent busy ports

hi, i would like to know if there is any way i can get around the "address in use" error i get. See i want to be able to have multiple windows of my program open, all listening to see if a message comes on a certain port,,, but that gives me an error saying that you can only listen to one port at a time.... so does any 1 know how i can write something that tells me that the port is "busy" and then switch to listening to another port instead?? plus if i switch to listening to anotehr port, how does my client know which port to send to??

thanks in advance!