There are several different types of Special Forces in our military. These include:

Army Rangers - small units of up to a several hundred men. They're heavily armed and typically perform direct action (DA) missions where they go in, kick ass at a particular objective, then leave quickly. Here's a link to the Ranger Handbook to give you an idea of what they're all about.

Army Green Berets - very small units of 6-12 men in each "A" team. They can do several missions including reconnaissance and limited DA missions. Their primary mission is guerrilla warfare. They can go into an area and organize, train, equip, and lead friendly locals. In this role, they can handle forces up to battalion strength. They could prove very effective against the Taliban, either by working with the Northern Alliance and similar groups or by helping form new groups.

Delta Force - very black organization established for counter-terrorism missions.

Navy SEALS - very small teams organized to conduct reconnaissance and perform DA missions against limited objectives.

Marine Force RECON - similar to the SEALS and other commando units with the primary mission of reconnaissance.

Air Force Special Operations include missions like gunship (AC-130), special forces insertion/extraction (MC-130, MH-53 & MH-60), and pararescue. They also have a group called Combat Controllers who can parachute into a region and set up flight operations.

Of course, we aren't in this alone. According to reports, the British have sent in their ultra-elite SAS forces. I think their closest analog in US forces are the SEALS. Those are very studly dudes high on any sane man's "don't mess with" list.

I also heard the British are getting ready to send in Gurkhas. If so, Allah help anyone they cross.

There are other units that could prove useful in Afghanistan, such as the 82nd and 101st Airborne and the US Marine Corps. These outfits are perhaps the best trained and equipped for operations in that region. I don't know enough about the 10th Mountain Division to comment on them.