Hi Ryan,
First off, you will need to have Mac OS X 10.4.10 installed in order to be compatible with your iPhone. That may be the root of your issue.
Also, are you sure that you have everything required to activate an iPhone? Like an iTunes Store account set up, a working Internet connection, etc?
This article explains how to active your iPhone. Follow all of the instructions from this Knowledge Base article, and see if you have any success now: