Cause of Error trying to connect to Wifi?

I recently got a 700 MHz iMac, with 384 MB RAM. Previous owner had Ubuntu running in it, and had no sound. I installed an Airport card and did a fresh install of Tiger. It now has sound but I can't connect to the office router. It sees the router fine, but after I type in the password, I get a message saying "There was an error trying to connect to the router." How can I remedy this? The OS is fully updated. Incidentally I get the same problem when using my 867 Mhz Powerbook Titanium that also has Tiger. If I use a LAN cable from the router to each machine, I can connect fine to the Web.