I was on H1B since 2005 Oct. and got married in the same month, my wife came joining me from China in 2005 Dec and since then we haven't leave the states.
My baby was born in 2006 Oct. and is almost 3 month old.

Last year when I file 2005 Tax return I applied and received the Tax ID for my wife already, my questions is:

1.For year 2006 tax return do I file married and joint returns? Do I put my baby as dependent?(not whole year)
2.I haven't use W4 for my baby yet, do I need fill my baby in the form?

Thanks!

1) Yes, you should file Married Filing Jointly. Yes, you should claim your child asa dependent. You can claim her as a dependent for the entire year, as it is irrelevant when she was born, just so long as she was born in 2006.

2) You can add a dependent exemption to your W-4 anytime in the next two months. This only adjusts your withholding a little bit. If you do not do it, your refund will only be bigger next year.

Thanks a lot for your answer!

Glad to help!