First things first - do you know if the network card on your new machine is working properly? When you connect directly to the Internet via your modem on the new machine, are you using a USB connection or are you connected via your network card?

From the problem you suggest it sounds like the network card and the router aren't functioning together correctly - this may be down to old network card drivers or a problem assigning an IP address. It is a strange problem as two XP machines are working quite happily with your current setup.

The first thing to do is to go into Control Panel and look for your network settings. From here, you will be able to see whether or not your computer is connected to the router. If it is, then you will be able to right click on the wireless network icon and select properties. Using the tabs, you can see if your machine is connected to the network, if it has successfully sent and received data and if it has been assigned an IP. If a wireless network icon appears but you are not connected, then it is probably a configuration problem. If a wireless network icon doesn't appear, then the problem is a little more fundamental and may be solved by reinstalling the card and/or updating drivers.

Let me know how you get on and I'll try and answer any questions you might have along the way.

John