Hi,

I arrived here on H1 in August 2008 and my wife and son joined me in September 2008, both on H4. Now while filing taxes for 2008, can I file under "married and filing jointly"? If so, does my wife/son need an SSN? If so, how do I get one for them? I see that most websites are asking for their SSN's..

Thanks in advance,

You need to submit Form W-7 with notarized photocopies of their passports WITH the tax return to get them Individual Tax Identification Numbers.

You can file joint return as residents but you must wait to file your tax return till you complete SPT in 2009.
Read Your U.S. Tax Return: Substantial Presence Test