linksys wrt610N and airport card no go for WPA

I just installed a new Linksys router to run my wireless network with 4 macs. The 2 macs running 10.5.4 with airport extreme cards worked right away. The PB G4 (12 inch) with airport extreme initially would only connect with security off. Finally I temporarily enabled SSID and the PB could connect with WPA Personal.
But I still cannot get a G4 Cube with original airport card to join the network except when security is off. Using WPA Personal I get "the wireless network does not support the requested encryption method". The Cube OS is 10.3.9, Airport app is 4.2; so it meets Apple's WPA requirements. I know it won't support WPA2 so I've bumped down wifi security to the lowest common denominator ,in this case WPA Personal. Has anyone gotten an original airport to work with WPA? Or know of a USB wifi adapter supporting WPA for the Cube?