Airport woes - please help

[tck]

My snowbook (10.2) has problems with joining any wifi network - and I could
really use your help please.

The settings:

* Airport sees a network with name and base station ID which I can join
* Status: reported as not available
* Network: set to automatic location, show airport. TCP tab: set to DHCP, IP
address is there, Subnet mask is there, Router is there, DHCP client ID
shows nothing, Airport ID is there. Airport tab: tried both, join best
signal or specific network
* Assistant setup works, sees network, says ready to join

Result: Irrelevant of what I try to do, browser always says ³server not
found².

What¹s going on, or what am I possibly doing wrong?

Many thanks for your input,
Tobias