Connnect the WRT54G directly to your computer.
Set your workstation network adapter to a static IP of 192.168.1.2, subnet 255.255.255.0, gateway 192.168.1.1
Start IE and go to 192.168.1.1
There is no username, the password is admin
I believe the Voyager gives out DHCP address in the subnet 192.168.0.x, so set the WRT54G to a static IP of 192.168.0.2, subnet 255.255.255.0, gateway 192.168.0.1
The find the DHCP settings, and disable DHCP on the router.
Set the same (B)SSID as the Voyager, but set the WRT54G to a different channel.
Apply all changes and Exit IE. Shut off power to the Voyager and the WRT54G.
Now take an ethernet drop cable and go from the Voyager LAN port to the "Uplink" port on the WRT54G. Power on the Voyager. When the lights stabilize, power on the WRT54G.
Set your workstation network adapter back to "Obtain an IP address automaticly".
Start, Run, ipconfig /all /release
Star, Run, ipconfig /all /renew
See if everything is working OK.