Do the IPCONFIG /all command again, and take a note of the default gateway for the BT Voyager.
MAIN PC Configuration
BT Voyager settings - leave alone, they are fine
Onboard LAN Settings
Control Panel > Network Connections > Right Click 'Local Area Connection (your onboard LAN) > Properties > Click (once) Internet Protocol (TCP/IP) > Properties button > Click 'use the following IP address'
Enter the IP address: 192.168.0.1
Subnet Mask: 255.255.255.0
Default Gateway: Write down the BT Voyagers default gateway and copy it here.
DNS Server: Again, copy the BT voyager's default gateway here
Alternative DNS Server: Leave blank
Advanced Button > WINS tab > Tick 'enable NETBIOS over TCP/IP'
Second Computer's configuration
Control Panel > Network Connections > Right Click 'Local Area Connection > Properties > Click (once) Internet Protocol (TCP/IP) > Properties button > Click 'use the following IP address'
Enter the IP address: 192.168.0.2
Subnet Mask: 255.255.255.0
Default Gateway: 192.168.0.1
DNS Server: 192.168.0.1
Alternative DNS Server: Copy your BT Voyager's default gateway here
Advanced button > Add button (under default gateway) > Enter the BT voyagers default gateway here as well > WINS tab > tick 'enable NETBIOS over TCP/IP
And hey presto, both computers should have access to the internet. Sorry, this is a bit rush typed! If theres anything you need clarifying, then just ask!