Server Not Found Error Message

[arnold.pietersen at cecs.org.za]

I am connecting wireless to a network called "conferences".  I do
get
an IP address, Broadcast address, Primary and secondary DNS.  When

typing ifconfig, I can see ath0 and wifi0 and there is activity.
But
when I go to Firefox it says: Server not found

I was given the website address for authentication which I typed at

System -> Preferences -> Network Proxy.

Any help

Arnold