I recommend you look at the OSDev wiki. It is a fantastic source of information regarding programming an OS in many languages, including c++.
Specifically, see this section which tells you just about everything necessary to get going with a c++ kernel using gcc.
Finally, check out the OSDev forums, there are lots of users there ranging from newbies to highly experienced. They are usually more than happy to help people (so long as they show they tried before asking :-P)
