Spoofed IP address

Thanks everyone who read and answer my question.

Given a scenario as below:

When someone wants to launch a man-in-the-middle attack on the 
communication between the client and server. In order to make it more 
transparent(hard to discover) can the attacker pretended to has the same 
IP address as the server(when handling the communication with client 
end) while pretending to has the same IP address as the client(when 
handling the communication with server end). If it is possible, can you 
tell me your solutions.

This is not used to generate real attacks, it is just a concern I come 
cross when designing a communication system.

Thanks a lot.

Xun Dong

------------------------------------------------------------------------
This List Sponsored by: Cenzic

Need to secure your web apps?
Cenzic Hailstorm finds vulnerabilities fast.
Click the link to buy it, try it or download Hailstorm for FREE.
http://www.cenzic.com/products_services/download_hailstorm.php?camp=701600000008bOW
------------------------------------------------------------------------