@SkyDiploma: Man.. you are evil!
@racoon: Stay away from the evil temptation of making your own class named string in the std namespace.. if there is a Hell for programmers this will certainly send you there.
@firstPerson: That's because YOUR compiler lets you do that. vc++ 2010 will not.
@Sky: You still have to include the header file for your version of the string slcass. So its not even "technically possible". You need to include the string header file regardless of whose class it is (or put your class declaration in the *.cpp file that uses it)
@Sky: But that's not answering the OP's question. I think he wants to use the string class that's in STL. Writing your own isn't the same thing, nor would it even be desireable outside the adademic area of a university.
You could of course write your own string class, and use it in any way that you please, as long as you don't put it into the namespace std. (Or if you do not use anything from the namespace std anywhere in your entire program; very difficult indeed - how do you get rid of std::bad_alloc?)