Harley Hahn's Internet Exploration Station uses a facility called "frames". In order to visit this site, you need to have a browser (web program) that supports frames.
If you are seeing this message, it is because your browser does not support frames. This is probably because you are using an old, obsolete version of your browser (such as an old version of Netscape Navigator).
The best thing for you to do is install a newer browser. (This is generally a good idea anyway.)
You can get a new browser for free from the AT&T WorldNet upgrade area: http://www.worldnet.att.net/care/upgrades/.
Once you have installed your new browser, please come back and enjoy Harley Hahn's Internet Exploration Station.