OS X :: Accessing Home Internet While Away?

Without going into too much detail about the crazy logistics of the two networks that are available here, this is the situation:

Up until last Sunday (it was working fine at about 11:45 Saturday night right before I left), I had always been able to use one particular network jack. I'd just plug in my RJ-45 (Cat 5) cable and power up the MB and be on my way. Well, when I came in on Sunday, the jack is dead. There are other jacks to this network in the building, but the closest one is about 75'-100' away. I'd just buy a longer cable, but I don't think they want me running RJ-45 across the office when I need to use it. Not only that, but the company that supplies that network will be moving out in June, and most likely shutting off all their jacks in the building.

Now, we have the other network here that is obviously still working, but I do not have the credentials to connect to it. When I plug in the network cable, I get the familiar "None of your preferred networks are available" dialogue box.

So my question is this - is there some way that I can tap into one of the existing networks and bypass the company stuff by just connecting to the Internet through the DSL account we have at home? I mean, if you have a network jack that is working, you don't need to have access to that particular network to get out onto the Internet as long as you have a login and password to a network, right?