I came to US in May'06. My wife & son were with me during the first half of 2006 in India. They both have valid visa to travel and will join me soon. Can I claim my son as dependent? Also can I file jointly with my spouse? Appreciate your answer

You CAN file jointly with your wife if you and she are choose to be treated as resident aliens for ALL of 2006. Your wife's physical location during 2006 is irrelevant for this option. Note that, by choosing this option, you make your India-based income for 2006 subject to U.S. taxes.

You cannot claim your child as a dependent, however, as he has spent NO time in 2006 within the U.S.