Laptop wont connect to wireless internet

Hello,
my laptop is a compaq presario v2000 (windows xp) . i went to the public library a couple days ago and wanted to use the internet. my computer found the the network and everything. i connect just fine but once i tried to use the internet it would say that i dont have a connection. i choose the "diagnose connection" button on the page and would say that something is wrong with the dns... i reinstalled the wlan software and everthing in my computer and reset to default settings and still nothing. any suggestions to wat i can do to fix it??

thanks, junior