With most routers, you will require a PC with an Ethernet port.
I got a PCI Ethernet card for one of my PCs for well under £10 and it auto-senses the speed of the network connection - works great!
Once you have that in your PC, you will need to move it into the room with the telephone line to get the router setup.
Then disconnect the ethernet cable and set it to work with the wireless USB adapter as well (in the same room).
After that you can move the PC back into the other room.