(1) The router will not work with you old PC because almost all routers use netwrok (ethernet, lan) connection, not usb. Of course, you can fit a network card for a few pounds. If you planning to add more machines on your network, router/access point is a good option.
(2) For two PC, you need so called ad-hoc peer to peer network. One wireless card for Laptop, same one you saw, one usb wireless stick for old PC, you can find this in dabs.