I entered the U.S. as a permanent resident two months ago, but have still not received my green card. I'd like to take a trip back to Pakistan to see my family -- what can I do to make sure I'm allowed back in?
Some people wait many weeks or even months for their green cards -- apparently putting some plastic over a photo is harder than it sounds! In any case, your lack of an actual green card shouldn't stop you from traveling.
When you entered the U.S. as a permanent resident, you should have been given a stamp in your passport to show your new status. Double check your passport to make sure, but they're unlikely to have forgotten -- if they did, make an INFOPASS appointment to go to the nearest office of the agency now called U.S. Citizenship and Immigration Services or USCIS (formerly called the INS). Take your passport and paperwork.
The stamp in your passport will have an expiration date on it, usually within six months. As long as the expiration date hasn't passed, and won't pass while you're away, you are free to travel.
Here are a couple of other useful precautions: Check the expiration date on your passport itself. If your passport will expire while you're away, get a new one -- but carry both the old and new one with you, since the old one has your permanent residence stamp. Also, leave a photocopy of your passport and permanent residence stamp with someone who will be in the U.S. while you are away, in case your passport gets stolen or lost. (If it is, you'll need to go to the nearest U.S. consulate. Having a fax of your permanent residence stamp will help enormously).
One last thing to remember: You shouldn't stay outside the U.S. for more than six months, or do anything else to indicate that you really intend to live outside the United States. People can lose their permanent residence by "abandoning" it. For more information on traveling as a green card holder, see Nolo's articles on, "After Getting Your Green Card: How to Keep It."