Macbook - unstable network connection

Dear Macrumor users.

I will gently excuse myself if this has been asked before - I believe it has some years ago, but I haven't heard of my example yet.
What happens is that i attend a school, where we are 700 people using the same internet. Actually it's divided into 4 sections, so there are probably 250 in my group. This network is protected by a WPA2 password, and has additional login forms, which gives the school the ability to check all in- and outgoing transfer. However, I have lately been getting some problems connecting. What happens is that I connect, and it works for about 2 minutes. Then, it just won't load any sites and just keeps trying to load until it finally admits that it can't retrieve the server. It's my third year. and I have never experienced this before, so I thought: Well, gotta be the school's internet, but i haven't heard of any other ones having this problem. This makes me worried that my macbook's airport extreme card is broken.

I was wondering if anyone had experienced a similar problem, or maybe could give a hint towards a solution?

I am running a 13 inch macbook unibody (the silver one), with the newest system and all upgrades installed. Problem is: The airport extreme card is located in the display. I don't get why, but it makes me not want to change it myself, should it be destroyed.

Please help me!

Kindly

-Frederik

Edit

Well, I finally took the time to set up Little Snitch and it seems to have done the trick. I have blocked all wi-fi's expect those on the local network, and I guess that solved the problem. If anyone should encounter this problem, i'd recommend setting up LS.