Please don't take this as condescending - I say it because I made the same mistake myself! Did you actually install the developer tools when you installed ArcGIS? I made the mistake of thinking I had when I really hadn't because I assumed it would have been installed with a complete ArcGIS install from the installation source I was given.
But in the case of the ArcGIS distribution that my university uses, the developer tools were not included with the .msi installation tool that was distributed on the school's software installation website. I had to the actual installation DVD in order to install it (my university provided it as an ISO).
Double check your installation source DVD, run ESRI.exe, and then make sure the sources you need from "ArcGIS Desktop Developer Resources" are fully installed.