Plain text password

Hi All ,

 I have setup SSL for my virtual setup. Now only for the 

knowledge purpose i want to know if i dont use SSL and then try to acess the mail file . Now suppose i give my user name and password i belive it goes in simple plain text. How can get this normal plain text during the transmission over network. Is there is any software is required to hack information passed on n/w if it is not encrypted ? if yes how can i setup it . Please suggest me from where to start to achieve this .

Vikalp