I'm not sure exactly what your question means so I hope I'm not on a tangent. Correct me if I'm wrong but isn't this song famous for not actually being in one key?

Here we go I remember this from ages ago:
http://guitartricks.com/forum/showthread.php?p=216468&highlight=gimme#post216468

That explains the song. Basically half of it is in C#, the rest is in C#minor.