Accessing the Internet on a WEP enabled Toshiba Wireless LAN

I have set up a peer-to-peer wireless network at home. Three portables and a desk-top. The desk-top is attached to an Alcatel ADSL modem and the portables access the ‘net using Internet Connection sharing. When WEP is disabled and the network unsecured all portables work fine. When enabled, a Toshiba Tecra and an IBM work well but an older Toshiba Satellite 4600Pro cannot access the net. The buit-in Wireless card on that Satellite uses a driver from Lucent version 7.43.0.9 and the Operating System is XP. Do I need to upgrade the driver or ….?
Thanks