The dialect that Rosetta Stone teaches is Modern Standard Arabic (MSA). This is the broadcast standard language used on Al Jazeera TV, as well as the standard of business, government, publications and educational institutions. It is very similar to Egyptian Arabic and evolved from the classical Arabic used in the Koran (Qur'an).
Most Arabic speakers use a combination of MSA and a colloquial dialect that reflects regional and socio-economic factors, depending on the formality of the setting. A student who masters MSA will have a solid basis for communication, but should be prepared to expand his or her knowledge to include colloquial dialects.
The Arabic alphabet contains 28 characters that directly relate to the sounds they represent. At this time, there is no standard version of the Arabic alphabet that uses Roman characters (i.e. those used in the English alphabet).
In most contemporary Arabic countries you would typically see Modern Standard Arabic written without vowels (although you do not see the vowels you still pronounce them). The Arabic with vowels is useful when learning the language because it helps you to recognize the distinct sounds that influence the pronunciation and meaning of a word.
Although it may seem difficult to learn both a new alphabet and a new language at the same time (especially one that reads right-to-left), Rosetta Stone's immersion based learning method facilitates the process by simultaneously developing your listening and reading skills while you learn the vocabulary of the language.