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.
Step 1: Do everything beforehand
Step 2: Setup the hardware