Ivano,
As Sander rather concisely said, its a bit difficult to advise you when your questions cannot be put in the context of an eventual goal that you would like to accomplish. i'm sure that if you were to take a few moments and write down some information about the projects you'd like to do, that someone here shall be able to advise you. Its easy to say you wish to use it for Art, yet what in what sense of Art exactly does that mean? Fractals, Cellular Automata, Image Processing, Show Control, etc.?
As you can see as you read further, I put some time into writing this answer for you; for all of us here, please help us to help you by doing the same.
You can do a search on using the terms Mathematica, Wolfram, and Art to find interesting articles such as this one by the [Wolfram Blog Team
Creating Escher-Inspired Art with Mathematica][1] Indeed, just scan the Wolfram and WolframAlpha blogs and you'll find a number of articles having to do with Mathematica's impact on the Art World, both locally and Internationally. And, since i saw the exhibit in the National Science Museum in London, I also seem to recall an article some place about generating patterns in Mathematica for crocheting works depicting non-Euclidean geometries. Just try it, you'll see a number of articles out there.
On the iBooks store there is a short book covering visualization with Mathematica. i cannot recall if its free or not yet I will say that its a very pretty book. Finally, the Wolfram Demonstrations project is the place to go to see some of what is possible.
In general, questions like yours are pretty much Yes when considering most of todays programming languages. However, Mathematica makes it quick for you to envision and test some very complex things in a very few lines of code. Often times, when moving at the speed of todays 'Art' you need this 'rapid prototyping' simply because, without such, you can't even decide if what you wish to do is possible at all.
Realistically, regardless of whether you decided to leverage Mathematica or not, you absolutely will use other languages and technologies. There are no silver bullets per se.
If you have an interest for generative art, then Mathematica is a great system for you because it excels at all things having to do with 'The Book'. And, If you get that reference, then Mathematica is definitely, definitely for you :-) Learning and using it is far better than waking up one day to an unfamiliar ceiling (Another reference specifically for Fans of Japanese media arts[i.e. Anime]).
Ciao,
Dave