C++0x == C++11, and you can see what version of GCC has what here:http://gcc.gnu.org/projects/cxx0x.html
It all began with GCC 4.3
Note that some of these features were reworded in newer drafts, so there may be a difference in behavior between 4.4 and the newest (probably correcter) behavior. If you are going to use C++11, I suggest using the latest GCC version (4.6) to guarantee the best compatibility. If possible, also compile your code with Clang, which also has pretty solid C++11 support, and very good Standards compatibility. Plus, it points out your errors as exact as it can. I don't suggest using (64-bit) binaries produced by Clang on Windows, support for basic stuff is flaky in some areas (exceptions, dllexport...).
If unsure about some syntax or behavior, your best bet is Stackoverflow, there's a lot of knowledgeable people there, if you ask a good question ;-)