I’m Doing a Dissertation on Sign Language and Need Help?

First, you´ll have to choose between two theories: sign language as a second language or as a foreign language. It´s all a matter of opinion because, quite frankly, there are good arguments on both sides. My personal opinion favors the first. Long story short, whenever we talk about languages (second or foreign) we have to consider the learning situation. According to Douglas Brown, people learn second languages in host countries (that is, someone learning English in an English-speaking country) and foreign languages, in foreign countries (for example, someone learning English in China). As you can see, culture plays an important part in both situations. In second language learning, the learner is in direct contact with the second culture but, in foreign language learning, he is not.
All users of sign languages were born and raised in a certain environment (the U.S., for example). Therefore, American culture is their first culture. Since they have some kind of hearing impairment, they learn to communicate with their peers, with whom they share the same cultural background (= their second culture). Since language and culture go hand in hand, their sign language is their second language. In addition, just by watching people talk and/or by reading lips, these individuals, ever since they were born, have been exposed to English (to a certain extent).

Here are some sites that may help you:
ASL (American Sign Language):
http://www.deafllibrary.org/asl.html
http://www.nidcd.nih.gov/health/hearing/asl.asp
http://www.lessontutor.com/ASLgenhome.html

BSL (British Sign Language):
http://www.UltraSites.cc
http://www.EveryRule.com
http://www.learnbsl.org/

Good luck! Very interesting topic you´ve chosen.