Look for site, and Redirect if 404 or other error

[MikeG]

I'm trying to write a script that will run via a web browser on a
local machine. The intent is to determine if a the machine in use on
an internal network or the Internet.

I need a script that:

1) trys to connect to a specific site
2) If that site can't be reached for whatever reason tries a different
site.

Any ideas?