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Windows XP Pro includes functionality to access the computer's desktop across a network. Remote Desktop must be enabled and configured properly.
How Can I access my Windows XP Machine Remotely?
Terminal Services and Remote Desktop that are available in versions of Windows NT, 2000, XP and 2003 are all about accessing your machine remotely via your network connection. Across the room or across the country it's almost like being right there.
Both Terminal Services and Remote Desktop allow you to connect to a Windows machine over a network net and get a full desktop. It's almost like being at the real console. In fact it's so close that it's allowed many people using multiple computers to set some up without any monitor or keyboard installed at all and use remote access only.
Terminal Services, originally code named "Hydra" after the many-headed beast of Greek mythology, is a technology incorporated into Windows NT servers that allows multiple clients to connect to the machine at the same time. Each connection creates a new "virtual" desktop complete with all the icons and menus that you'd see if you had actually logged on on the machine's console. The only downside is that prior to Windows 2003 Server you could not actually log into the actual console remotely.
Enter Remote Desktop in Windows XP Pro. Remote Desktop uses similar technology to allow you to log into a machine remotely but you can only log into the one true desktop - there is only one session. If you log in remotely using Remote Desktop, then the console session is disconnected. Conversely if you log into the console then any remote session will be disconnected. The good news is that if you log in using the same account applications remain running and you can effectively "move" the console to a remote connection and back again.
Windows 2003 server allows for both types of access: additional sessions and Remote Desktop.
In either case the keys to accessing a machine remotely are:
The machine you want to connect to must have either Terminal Services or Remote Desktop sharing installed and running.
The machine you want to connect from must have the Terminal Services or Remote Desktop client installed. The Remote Desktop client is included in Windows XP and can also be downloaded for free here. It can be used to connect to both Terminal Services and Remote Desktop.
When you run Remote Desktop Client you'll specify the name of the machine to connect to and possibly some options controlling the connection. As long as you can "see" the other machine - meaning it's on your local LAN or behind some kind of firewall on the internet then the client connects and you'll be presented with the very familiar logon screen from that machine. Logon and you're there.
Once connected you can do anything remotely that you could if you were sitting at the machine with two very important exceptions:
If the machine is truly physically remote from you then you will not be able to do things like insert a CD-ROM or other physical things.
Windows must be running which implies that you cannot remote-desktop to the boot sequence or to change BIOS settings.
As I mentioned earlier, you can happily use remote desktop across the internet as long as the server is not protected by a firewall such as a broadband router. If it is and your firewall or router supports it you can open port 3389 on the firewall and forward that to the machine you want to connect to. Note that if there is more than one machine behind the firewall then only one can be connected to across the firewall this way.
And finally, Microsoft has a "how-to" article on setting up and using Remote Desktop on Windows XP here.