The easiest way to share a WI-FI connection is to have a network adapter for every singe computer you want to share the network with. But what is you only have 1 adapter, 1 connection, and 2 computers that you need to share the connection between?
You will need:
A wireless network adapter. (Preferably USB, but any will do)
An Ethernet cable (The same length as the distance between the 2 computers.)
Windows XP or better.
A wireless network.
And a general understanding of how the internet works.
My reason for needing a connection split between 2 computers is because I needed to move the router, and modem downstairs, where my family spends most of their time using the internet. So it would seem logical to move the router downstairs (to get better reception). However, I ran into a problem... The two computers in my room were connected to the internet using 2 Ethernet cords, and I only had 1 USB wireless adapter. To share the connection I would have to create a MAC Bridge between the Ethernet cable, and the WIFI adapter on the same computer, (while the other end of the Ethernet is connected to the other computer). So do everything you need to do before starting this, move the router, wires, and power supplies beforehand (and test that it works).