Q: iMac cannot connect to WPA2 network

My early-2008 iMac will connect to my wireless router only if I turn off WPA2 protection. With WPA2-PSK on, the iMac seems to connect, but generates the "No Internet connection" error with the exclamation point over the wifi icon in the status bar. In other words, it connects to the router, but cannot get an IP address. It works perfectly fine if I turn off WPA.