Yes, they specialise in counter-terrosism operations. No, they are nothing like Tom Clancy anything. The FBI HRT is not "Special Forces." The only "Special Forces" within the United States is the US Army Special Forces.
The FBI HRT trains in CT and HR and are a full time team, which makes them more specialised than the FBI's SWAT teams - but are capable of performing your average SWAT duties as well, obviously. They often train with the military and other federal and sometimes local civilian tactical teams. Their selection process is about two weeks, training after is about 4 months and one has to have been a special agent with the FBI for 3 years before even applying. (I'm about 95% sure that's correct, but you can always check on the FBI website to make sure) When not deployed (CONUS) they train full-time. So, you can tell right away the initial selection and initial training time is much shorter than that of military SOF units. A lot of things are different, these guys are federal law enforcement, not military .. so there are going to be different SOPs and a different mindset. I've trained and worked with them a few times, and they are very good, but it's really hard to compare a law enforcement agency to a military unit.