I see...

Well you not owning the router change a lot of things. If it's a big complex the connection could be split in Access point (sort of relay for the signal). If you get 4 out of 5 bars most of the time the problem is more than likely not with your card since it's picking up a strong signal. I would check with the owner of the complex and try to get them to help you out.

The antenna I mentioned might be something they want to look into. Depending on their knowledge of Wireless it could be a nice setup but if it's a multi stories building so many things can happen between the source and your card (phones (which work on 2.4Ghz range now a day), signal lost, noises.

Checking with them would be my first step as if you have a solid connection and it drop all of a sudden and come back at full strenght the problem is more than likely not on your end. To say that I'm making the assumption that your computer location doesn't change (i.e. a laptop that you move from room to room while connected)