Having said that, I will explain the set-up. My home had a server and mail server. Now we just have a cable connection with our local cable co. Both showed the same symptoms: If I set my uploads to high and lots of users connected, OR if I was downloading lots of content, the internet connection become similar to a connection via the phone line! I use a iBook connected via airport, other users connect directly via ethernet cable.
If your landlord connects all of the apartment buildings off of one cable modem, then I would complain- unless you dont pay a lot for the cable connection. Sounds like you should be paying the price of a phone connection.

I do have one question for you though: When you browse the internet do the pages load fast? If they do load right away then it might just be limewire, but if everything you do online takes forever, then it is your internet connection.