Hi,

I came to US in Dec-2009 on L1 visa.
My wife and child came on June-2010.

I would have to fill the W4.
Since my dependents does not complete 183 days. Will they be treated as Non-Resident Alien.

I have compelted 183 days so I become Resident Alien.

Q1. There is option for line 3, with the note.
Note. If married, but legally separated, or spouse is a nonresident alien, check the “Single” box.
So in this case shall I fill Single or Married.
1.a... if I select single will the extra tax deducted?

Q2. If my dependents does not complete 183 days in US, can we still file taxes jointly?

For the 2010 tax return, you will file jointly with your spouse and you BOTH choose to be treated as resident aliens, claiming your child as a dependent on the return.

On the W-4, claim MARRIED status with TWO allowances, Under special IRS rules for foreign nationals, TWO is the maximum number of allowances you are allowed to claim. This is done to ensure that enough taxes are withheld from your salary to cover any tax liability.

Yes, you can file jointly with your wife even if she never sets foot in the U.S. To claim your child, the child must spend some time in the U.S. in 2010.