On my Mac at home, I've been accessing the app that I've been building with "Simply Rails 2" at localhost.

Never been a problem

I'm using my brother-in-law's Mac temporarily to progress the project. On his Mac, I can access the app at 0.0.0.0, but not at localhost or 127.0.0.1

It's not a deal breaker, but I'm curious. What could be happening here?

Both are running Mac OS X 10.5

(All on port 3000. URLs are truncated because the forum software doesn't me to submit links.)