If the computer is vista, you can....
rightclick the icon NETWORK
go to properties
click on "manage connections" on the left hand side
once you can see your available network connecitons, you can rightclick on the wireless network, and select properties
change the tab at the top to "sharing"
tick the box that says "allow other network users to connect through this computers internet connection"
if the computer is XP you can try following the below link - which is very similar to the instructions above
http://support.microsoft.com/kb/314066
