To enable Internet access to all PC's you will need to use a software program to set one PC up as a server. Im assuming that you have one PC set up for Internet access or you wouldn't be read this. This PC will needed to be set up as a server.
You will need to purchase a Internet server package. I suggest you use Wingate as it is relatively easy to set up and it is extremely reliable. You can download an evaluation copy from Wingate which will be good for one month, which is plenty of time for evaluation. The documentation included with the package is excellent. I've tried many other packages but none stack up to Wingate.
Please support this software and purchase it if you find it useful.
Don't go and download a crack from Astalavista to extend the the evaluation period to indefinite.