suddenly lost wireless internet.....

Here is the issue: The university which I attend has two wireless networks; a guest and secure (802.1x). My 15" powerbook 1.67 running Tiger never had issues before, that is until last week. All of a sudden it won't work! With internet connect open, it shows that i'm indeed connected to the network. If I open safari, the first window will load, and possibly a couple more, but then it hangs and displays the "your not connected to the internet.......would you like to run Network Diagnostic" or something to that affect. So, I'll run network diagnostic and on the left it has the list (isp, airport, network settings, internet, server, etc...) which shows all green except for the "internet" and "server", which are red. If I allow it to go through the diagnostic it will show," it appears that your internet is working properly" or the like. Then it works again for about 3 pages worth of loading....then hangs. When the internet isn't working, if I open network prefs, tcp/....and click DHCP renew, it will work briefly (3 pages or so), but then quits again. I have to either continue to renew DHCP, shut airport off/on, or go through the diagnostic to get it functioning.
My internet at home works, however, it does seem slow. I've tried trashing plist. files, permissions repair, and resetting PMU, all of which were suggested around the internet, but to no avail. So, what the F***??? The hacks at the tech dept. didn't know what to say to me, so i'm turning to MF.
Any suggestions? Oh, i was going to take my airport card out and reinstall, but I couldnt find instructions on how to do it for my particular model. Something tells me that it wouldn't help anyways. TIA