It would be really strange if he is presently surrounded, and was to die on March 2 - because that is Ashura day, when the martyr Hussayn was killed along with all his followers, after being pinned down for several days. A very famous story in the Shi'ah world.
But Bin Laden is a Sunni not a Shia. I wonder if the Iranians have come up with this story because they are in the Ashura season and it is playing on their minds.
I don't believe these stories about Osama surrounded, because he doesn't strike me to be as much of a puss-boy as Hussein. He'll kill himself.