can you tweak/hack a cable modem?

I'm getting cable at my house (FINALLY!!!). But it's 256 download/128 upload. They gave me the modem with no drivers, mauals or anything. The cable company told me that I just plug it in my pc and it works. So I was thinking there are 2 ways they control your bandwith
1-. the modem is pre-configured to max at the bandwith they set
2-. their router have on each nod (sp?) capped to 256kb

I didn't find anything on sharky, so if this is against the AUP go ahead and close it. :)

I think it will be illegal to do that. I will not post any programs that can or will help you do it either.