Your USR device does appear to be a wireless router. However, to use a router which doesn't have a built-in ADSL modem, you need to use a separate ADSL modem which supports an ethernet connection - you cannot use a USB modem with a router. It is the router which connects directly to the ISP, not the PCs which get their internet access via the LAN.
At the moment, you can use it as a basic "wireless access point" by connecting it to your main PC by ethernet cable and to the laptop wirelessly.
You will then need to set up "Internet Connection Sharing" on the internet connection of the PC with the modem attached. When you set up ICS, the 'host' PC acts as a DHCP server to allocate IP, Subnet, DNS and Gateway addresses to the 'client' which has its network adapter set to get addresses automatically. The problem is that a router also allocates addresses to the networked PCs so you need to disable its DHCP server to avoid a conflict. You might get away with giving the 'client' PC a fixed IP address, although ICS can be temperamental with fixed IPs.