Help needed! Cannot share internet connection

I am sorry if this question has been asked before. I am experiencing a problem with my connection. I recently bought a laptop with windows vista business and want to share a connection with my brother's desktop which using windows XP home. For convenience, my brother set up a wireless connection for me. But after a while we realized that the wireless connection make the LAN connection on my brother's desktop disconnected all the time. So we bought an ethernet cable for the modem. We think that it will solve the problem. But another problem appeared, the modem won't let us connected for the same time. Sometimes it is my brother's desktop who got connected to internet nd sometimes it is my laptop who got connected. It is windows vista issue? Or is it the modem issue? The modem was from Aztech. Help is very appreciated. Thank you very much.

 

A modem is for one purpose, connect to your ISP. To share connection you need a router connected to the modem. ( Note some modems are also routers, if so clone your mac address). Then you can setup the router to make the isp connection using one MAC Address of your choice, normally this is the pc used to setup the account. You clone that MAC address into the router if your ISP requires it, does not hurt, is just good practice. Then both pc's connect to the router using wireless or LAN connection. Your pc's now will have a private IP address, you get a NAT SPI Firewall for added security.