I have the following machines and having trouble connecting both of them wirelessely to the internet. Previously I had no issues with the Macbook connecting to the internet.

Machine Name: iMac
Machine Model: iMac6,1
Processor Name: Intel Core 2 Duo
Processor Speed: 2.16 GHz

Machine Name: MacBook Pro 17"
Machine Model: MacBook Pro1,2
Processor Name: Intel Core Duo
Processor Speed: 2.16 GHz

Optus Modem SurfBoard SB4100 Cable Modem

Can connect and see my wireless network on both machines and can set up computer to computer network hence the Airport Express is working OK, but when I set added the iMac I lost connectivity on the Macbook.

Any help would be appreciated.