You have to enable ICS (Internet Connection Sharing) on the machine where you have the Internet connection.
On that machine, go to Network Connection. You will find at least two Local Area Connections, One connecting to the ISP (Internet Service Provider) and the connecting to your LAN. Right click on the connection that connects to the ISP and click on Properties. Go to the Advanced tab and check the Internet Connection Sharibg check box. It will automatically reset LAN side IP address to 192.168.0.1.
Click on yes when it asks for confirmation.
Go to other PC where you want to access the Internet, go to TCP/IP properties and choose the radio button ‘Obtain an IP addrerss automatically’ and obtain DNS Server address automatically’.
That’s it. It will enable all the computers to access Internet simultaneously. Please let me know if it solves your problem