Purush,
I will not say the comments you posted is totally wrong, but it is mis leading to some extent about the residency. You said "after 5 years in the US, you can file 1040" that’s not right. There is a substantial presence test clause in Publication no 519, which goes like this. For more information refer Publication 519, or go to site www.irs.gov
if you want the direct link here it goes http://www.irs.gov/publications/p519/ch01.html

Substantial Present Test.

You will be considered a U.S. resident for tax purposes if you meet the substantial presence test for calendar year 2007. To meet this test, you must be physically present in the United States on at least:

31 days during 2007, and

183 days during the 3-year period that includes 2007, 2006, and 2005, counting:

All the days you were present in 2007, and

â…“ of the days you were present in 2006, and

â…™ of the days you were present in 2005.

Example.

You were physically present in the United States on 120 days in each of the years 2005, 2006, and 2007. To determine if you meet the substantial presence test for 2007, count the full 120 days of presence in 2007, 40 days in 2006 (â…“ of 120), and 20 days in 2005 (â…™ of 120). Because the total for the 3-year period is 180 days, you are not considered a resident under the substantial presence test for 2007.

The term United States includes the following areas.

All 50 states and the District of Columbia.

The territorial waters of the United States.

The seabed and subsoil of those submarine areas that are adjacent to U.S. territorial waters and over which the United States has exclusive rights under international law to explore and exploit natural resources.

The term does not include U.S. possessions and territories or U.S. airspace.

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