Uh, well, you are on 56k, right? The hacking will stop after you are disconnected. Also, your IP changes, so they cant really do it until they regain it again.
I have a good way to make your parents switch to broadband. It worked for me. Before connecting online, I would have kazaa, aim, icq, and other bandwidth sucking apps open when I would leave the computer. When a parent got on, they would get frustrated on how it takes like 5 minutes to open up a page. We very soon got broadband.