I am trying to configure a network between two computers, one running Windows XP Home Edition and another running Windows XP Professional. Both computers access the internet without problem through an 8 port router connected to a D-Link 302G ADSL modem. However, I cannot establish a connection between the two computers. Both computers are on the same workgroup, and disabling the firewalls does not make any difference. The network settings are configured to automatically obtain an IP address. How can I make the network work, so that I may use file and print sharing? Also, is it safe to use file and print sharing while on the internet?

This is quite a complex problem, so we need to work through the possible causes sequentially to narrow down the problem. Since the internet is functioning on both computers, this establishes the network interfaces are working. We must next ensure each computer is assigned a proper IP address. As the computers have been configured to automatically obtain an IP address, they should automatically obtain an address from the DHCP server running on the router (which distributes IP addresses to connected computers). To check the IP addresses on each machine, go to the ‘Start’ menu > ‘Run’ and type ‘cmd’ (without the quotes) then click OK. The command prompt window should appear. At the prompt, type ‘ipconfig /all’ (without the quotes) and press ENTER. The network information for the network adapters on your computer will be displayed. Under the entry for Local Area Connection, write down the ‘IP Address’ of the connection. Should the IP address not be assigned (the address is quoted as 0.0.0.0) or the address is in the range 169.254.x.x (which signals Windows cannot obtain an IP address from DHCP, so it has assigned its own address) this means the computer is not being assigned an IP address from DHCP. In this case, check DHCP is enabled on the router.

Assuming the computers are each assigned an IP address, we need to establish whether they can see each other. To test this, we will try pinging the machines. Before beginning this procedure, double-check the firewalls on both computers are disabled, otherwise the firewalls will likely block the pings. Then, on one of the computers go to the ‘Start’ menu > ‘Run’ and type ‘cmd’ then click OK to open the Command Prompt. At the command prompt, type the following command:
ping [IP address of other computer]
and press ENTER. For example: ‘ping 192.168.1.5′. If you receive replies (e.g. ‘Reply from 192.168.1.5′¦’) this means the computer can see the other computer. Then, try pinging that computer from the other computer to ensure it works both ways. However, if instead the request times out (e.g. ‘Request timed out’) this means the computer cannot ping the other computer. In this case, you have a network configuration problem. The possible causes are too detailed to go into here, so please contact me again should this be the problem.

Assuming you can ping the other machine (and vice-versa) the network is working correctly. We now need to ensure file and print sharing is installed and enabled on both computers. On each computer, go to the ‘Start’ menu > ‘Control Panel’ and open the ‘Network Connections’ control panel (you may need to first open the ‘Network and Internet Connections’ category). Right-click on your local area connection and select ‘Properties’. In the window that appears, click the ‘General’ tab. Check whether ‘File and Printer Sharing for Microsoft Networks’ is listed, and there is a tick next to the item denoting the item is enabled. Should the item not be present, click the ‘Install’ button to install this item.

Once file and print sharing is enabled on both computers you need to configure which folders you wish to share on the network. Right-click a folder you wish to share, and select ‘Properties’. In the window that appears, click the ‘Sharing’ tab. Tick ‘Share this folder on the network’ and give the share a name (preferably without spaces). If you want users to have full write access, tick the box ‘Allow network users to change my files’. Once you are finished, click OK.

To access this folder from the other computer, go to the ‘Start’ menu > ‘Run’ and type:
[IP address of other computer] [share_name]
For example: 192.168.1.5myshare. Then click OK. The shared folder should appear. You can also create a shortcut by right-clicking anywhere on the desktop, and select ‘New’ > ‘Shortcut’ and assign the shortcut the above mentioned location.

Regarding your question about the safety of using file and print sharing while connected to the internet, this should be safe so long as you take the proper precautions. In fact, this is what most people do since most have broadband connections connected directly into their routers. Since you are using a NAT (Network Address Translation) router, all your computers are assigned private IP addresses which cannot be accessed from the public internet, unless specifically configured at the router. This offers your first level of protection, since no one should be able to get past the router to the file and print sharing running on the network. However, as an added layer of security you might also want to re-enable the firewalls (e.g. ZoneAlarm) previously running. This will initially block all sharing, since the firewall is doing its job (preventing connections to the machines). However, if you setup firewall rules on both machines allowing access to each other, this should work.