parents visit & tax deduction

My parents (2 people) came to the US on Oct. 15, 2003, and will be leaving on April 11, 2005. They have been living with us in the US.

Could you please answer the following questions?

1. What is/are the regulation(s) on dependent Tax Deduction?

2. Can I apply ITTN for them, and claim my parents as our dependent to get some Tax deduction for 2004 Tax return?

3. Are we eligible for dependent Tax deduction for 2005 Tax Return?

Thank you for your time and help.