Stocks Practice Account

How can I practice portfolio investment without putting any money?
I am interested in learning investing in a portfolio but I do not want to invest money until i fully understand and grasp the concepts. I want to set up an account with “fake money” if that is possible and track my stocks and learn from my mistakes. Is this possible? I have checked out sites such as etrade, fidelity, and vanguard but they all require you to deposit in order to use the service and their investment tools.
Are there any sites out there where they offer portfolio softwares and analysis for free so that I can start learning based on how the market changes daily (rather than buying a book and reading the concepts, and never really using it in real life applications. )
Investopedia.com
Stock Market Analysis for the Week of 04/05/2010