ping outside the lan works (include dns), but browsers no!

Hi. I'm really new with linux, but I have a little experience. I have knoppix running in my work. 'till now, everything seems to be fine but, i have a problem with the browsers (konqueror and firefox). I set up my net config. and i can ping xxx.xxx.xx.xxx, I can ping www.wathever.com, and i can even go to ftp's with konqueror, BUT, when I try to go to any http, the browser (both of them) just can't find, said, www.google.com. In my work, we use a proxy, but the browsers just can find it when I use it in the browsers configs (in any of them) as I said, the net config is ok, becuase the ping's, and I insit that I can even go to the KDE ftp's that are in the favorites of Konqueror, but http://putsomethinghere.com, just don't work. I hpoe that you can help me .

Knoppik 4.0.2-En
Dell precision 650 2Ghz 1gb Ram
HD 80 gb in ntfs BUT, using a USB drive to write information