Good point. I assumed that by "man portable surface to air missiles", they meant "stingers". My mistake. While I am at it, here's some info on Stinger Missiles:
To clarify for other readers, the Stinger is a U.S. made MANPAD (Man-portable air-defense systems). If the Taliban have any, they are 20 year old missiles left over from the war with the Soviets, and they are most likely non-functional, since they have a limited life time. It would be embarrassing to the U.S. to loose aircraft to Stingers, but if there are any left that still work, there probably aren't very many, and the risk is limited. It's more likely that the Taliban has managed to acquire newer MANPADS (probably a Soviet design). This would be especially scary if these missiles were being supplied by the ISI or the Iranians, since it's then possible that the Taliban could acquire quite a lot of them.
http://science.howstuffworks.com/stinger.htm
http://www.designation-systems.net/dusrm/m-92.html
And on general MANPADS:
http://www.fas.org/programs/ssp/asmp/MANPADS.html