Have you tried just turning off all of the security for now to see if you can get on the network? Obviously only try this for a short while as this leaves you very open! Again, to re-iterate the point that you should use WPA2 if you can or WPA if you don't have WPA2 on your router. Are you in a position to try out someone else's wireless network to test your card in your Mac? Whenever I get timeout problems, I generally find it's my router to be honest and I have to just turn it off for a moment and then turn it back on and it seems to pick everything up.
The other thing I had to do in the past was to change the channel that the router was running on as I think it may have been conflicting with one of the other routers in the street and this seemed to make the connection a lot more stable.