I have 3 laptops and 1 desktop computer. I used 1 laptop as an ICS and connect the two laptop using wireless. These two laptops work fine and both can get the internet access. The problem is the desktop computer. I already installed TP-LINK TL-WN321G USB Wireless Adapter. It can connect to the ICS computer and also to the other two laptop, but still can not get the internet.
Probably time you bought a wireless router as you have that many computers. I assume you are connecting wirelessly via ad hoc network which is intended for swapping files between computers -- not, i suspect, for internet access.