Connection of PC to PC communication

hi all
kindly give me a brake down of hw 2 achieve PC to PC connection for the communication ie tru softphones and hw the softphiones ar configured 2 b seen as extension by the server PC.
Also hw is an IP address generated 4 each PC in the conection. i av only seen the installation demo on youtube, bt no clear xplanation on hw another PC is connected 2 it 4 cofiguration.
Pls, help as i need 2 demostarat it in my final year HND project presentatn

nd 0 *