They don't have the same IP address -- if they did, they wouldn't work (unless only one computer is EVER turned on at a given time).
Do you instead mean that, if you look at your IP from the outside, they all have the same public IP? That's normal, and unless you are willing to pay for multiple static IPs (which many ISPs will not give you even if you are willing to pay for them), you are stuck with your 1 IP.
So, in the usual fashion, I will ask you to please give as much information as possible about your setup -- I can't begin to come up with a solution based on the meager crumbs of info you gave!
-what type of connection, all the data you have about it, the settings it uses, etc
-what you want to do with the connection that leads you to want multiple IPs
etc.
tooki