Internet access is something you take for granted, until you have a group of computers fighting over one connection. If you're on the road with mobile broadband and looking to share it with colleagues, the most sensible thing to do is buy a portable wifi router that connects to a mobile broadband network and shares the connection wirelessly between multiple notebooks. If that's not possible, you can always use one notebook to connect to the internet and then share its internet access with other notebooks via wifi using Windows' Internet Connection Sharing options.

There are several ways to set up Internet Connection Sharing - you can access the web via Ethernet, wifi or mobile broadband and then share that bandwidth with other devices via Ethernet or wifi. Here we're going to look at sharing mobile broadband via wifi, as that's how you're mostly likely to use it when on the road. First a warning - Internet Connection Sharing can be flaky, particularly under Windows XP, so treat it more as an emergency measure rather than an every day setup.

The first step is to ensure your notebook's wireless card is switched on but it's not connected to any wifi networks. Next connect to your mobile broadband modem (probably a USB stick) to your notebook and then connect to the mobile broadband network. You should be able to do this with the software supplied with the modem. Use your browser to check you're online before proceeding.

If you're running Windows XP, open the Network Connections window in the Control Panel. Your mobile broadband connection should be listed under Dial-up - for example "HUAWEI3G.3 Mobile Broadband" - and the status should be "Connected". The status of your Wireless Network Connection should be "Not connected". Now right-click on the mobile broadband entry, choose Properties and then the Advanced tab in order to set up connection sharing.

Under the Home networking connection drop-down menu, select Wireless Network Connection (although you could choose Local Area Connection if you wanted to connect to another computer via an Ethernet cable or supply internet access to a wifi router via Ethernet). Now tick "Allow other network users to connect through this computer's Internet connection" and click OK if you get a warning about passwords. Click OK again, and then OK to the warning about some settings not taking effect until the next time you dial in.

Now you need to configure your "ad hoc" wireless network. If you're running Windows XP, open the Control Panel and then Network Connections. Right-click on Wireless Network Connection, select Properties and then the Wireless Networks tab. Click Add to create a new wireless network. Enter a network name, such as "ournetwork" and then untick "The key is provided for me automatically" and tick "This is a computer-to-computer (ad hoc) network". Now specify a 13 character password (the Network key) and then click OK. Click OK again to close the Wireless Network Connection Properties window.

Unfortunately Windows XP can only use WEP encryption for Internet Connection Sharing, not the more secure WPA. If you're regularly using Internet Connection Sharing, you should try to set it up on a Windows 7 notebook offering WPA encryption for Internet Connection Sharing, or you should invest in a WPA-capable portable wifi router.

Back at the Network Connections window, right-click on Wireless Network Connection and select View Available Wireless Networks. You new network should be listed, described as a "Security-enabled computer-to-computer network". Click on it and then click Connect, which will make the network visible to your other devices. You might find your network is more stable if running from a notebook rather than a low-powered netbook.

When you're finished you can disconnect from the mobile broadband network, then go back to your mobile broadband connection's Properties and disable Internet Connection Sharing. If you don't do this, your computer might keep asking you which connection you want to use even when you're connected to your home/office wifi network.

To start Internet Connection Sharing again disconnect your notebook from any wifi networks, connect to the mobile broadband network, share the Mobile Broadband connection via the Wireless Network Connection and then finally connect to your ad hoc wifi network.