You dont need a Belkin Disk to set up - this can be done manually
you can get a manual from this site
select G in the first dropdown and then your model - theres two to choose from and then then the version
you have a choice - you could change the comtrend router to just use the modem - bridged mode - they have a few different routers
see here http://www.comtrend.com/links/i$residential-adsl2-modem-router$product.htm
so not sure which one you have
if you can bridge to just use the modem then connect tothe Belkin and all PCs should connect to the Belkin
OR you can connect two routers together
Leave the comtrend router set as it is -
Set the IP address of belkin router to same subnet as the comtrend.
Depending on the DHCP range of the comtrend router - set the IP outside this range - so if comtrend is set to give an ip of 192.168.0.2 to 192.168.0.100 - set the belkin to 192.168.0.254
Disable the DHCP in the belkin.
Connect the comtrend LAN to one of the Belkin LAN ports - you may need to use a crossover cable.
On the belkin the WAN port will be left unconnected