I have been interested in alien (invented) languages since my first brush with elven in the Lord of the Rings. I checked out The Klingon Dictionary from the library in high school and currently own a copy of it and The Languages of Middle Earth. During high school, I nerdily amused myself by attempting to develop a language for Antarians, which involved gutturals and whistles. Speaking it myself was nearly impossible and I would occasionally practice, trying to go from a growling sound to a whistle as quickly as my human apparatus would permit. I imagine the average passerby might have considered calling the police to have me committed, or at least checked for rabies.
New Scientist has a brief article about the possibility of actually preparing for what alien languages might be like. The argument that Terrence Deacon of UC Berkeley makes (according to the article) is that language serves a purpose. It is a communication system for describing the world and since the world is in some way a fixed point of reference (though perception of the world is not), then abstract symbolism is a feature common to all languages.
At one point, the study of xenolinguistics would have been a dream job for me. A nice office at NASA, a field that will probably never be verifiable. Could you ask for more?