Your firewall is blocking port 9418.
Its not your machine's firewall then, its your local network
provider's firewall. Some ISPs may block non-HTTP network connections
in an attempt to stop illegal file sharing from taking up too much
network bandwidth. Unfortunately this also means their customers are
blocked from performing legal file sharing activity, such as
participating in an open source project. Talk to whoever supplies
your Internet connection about why TCP port 9418 is not being allowed.
There isn't much you can do otherwise. Longer term, we will have
better support for obtaining Git repositories over HTTP. The Git
project just started to test a patch series I wrote to enable
efficiently fetching/cloning over HTTP. I'm hopeful the next release
of Git will include this work, but that is unlikely to be released
before the end of 2009.