Get IP Address of Anyone Connected to my Arduino set up as server

Using Arduino Networking, Protocols, and Devices
11

Jeremy-arduino:
Ok, well I am on Windows 7 and I have not directory structure like that. The closest thing I can find is this:
C:\Users\Jeremy\Desktop\arduino-0022\libraries\Ethernet\Ethernet.cpp
C:\Users\Jeremy\Desktop\arduino-0022\libraries\Ethernet\Ethernet.h

I did do the edit on those files but I might not have put the code in the right spot because I got an error on compile:
sketch_mar07a.cpp: In function 'void loop()':
sketch_mar07a:47: error: 'class Client" has no member named 'IP_address'

I even closed all the sketch windows and save the files and then restarted the Arduino sketch. Is there a certain spot that the code needs to go in the files?

Jeremy

Ups... I'm on Arduino-18. :S LOL
Do you know where I can have a look at those Ethernet.c and .h files?