You have two choices
First: File nonresident tax return for 2008. You will get personal exemption and deduction as per tax treaty (depending upon your citizenship).
Second: Wait for about 5-months in 2009 till you complete SPT in 2009. The file joint return as residents. Read
Your U.S. Tax Return: Substantial Presence Test
About 401K: You must think again before putting your money in any retirement account. In 401K if you withdraw money before 59 1/2 you will pay early withdrawal penalty of 10% and the amount is your taxable income. If at the time of withdrawal, you are nonresident, the plan administrator will withhold backup taxes. You may even be required to file your tax return. If you return back to your country, then after you are 59 1/2 how will you manage transfer of funds from the U.S. to your country? And who will inherit it and will that person be able to manage your account.