I must admit that I am very thankful of the person who thought of the idea of remote desktop administration. I mean, I don't have to get off my rear to drive over to troubleshoot somebody's computer problems. Here are 3 methods used to connect remotely.
The first one I will talk about is CrossLoop which is obviously free. This is a really cool program, it allows your client, customer, or friend to create a code, then you type in the code on your side, and wammo you are remote into their PC. This is great but both parties, have to have the software downloaded and installed, so if you customer doesn't know how to do that, then you are out of luck. You can download CrossLoop at http://www.crossloop.com/
Method 2 which is also free, is Remote Desktop Connection. This comes with Windows XP. You can find it one of two ways, the easy way first is to hit Start --> Run and type mstsc, the other method is to click Start --> All Programs --> Accessories --> Communications --> Remote Desktop Connection.
This will bring up a window like you see above, then you just type in the computer name or IP address and click connect. If you want to use Remote Desktop Connection to connect to a computer across the WAN, then you will need to add a port forwarding rule to your router for port 3389 and assign it to the PC's IP address you want to forward the request to. You should then be able to type in the address to your router's WAN interface, not private interface and connect right into your PC. You might ask, "what if I want to RDP into more than 1 computer on a single network, but don't have assigned IP address?". The answer is simple, there are 2 ways to do so. You can setup as mentioned above, and once you are connected to your remote computer, you can open up another Remote Desktop Connection and connect to your PC from within the LAN. Basically a remote desktop connection within a remote desktop connection. The other method is to modify the following registry entry (PLEASE USE CAUTION WHEN MODIFYING YOUR REGISTRY, IF AT ALL POSSIBLE CREATE A BACK UP OF YOUR REGISTRY BEFORE MAKING MODIFICATIONS.) HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\WinStations\RDP-Tcp\Port Number, change this value to 3390 or something unique. Then on your router be sure to create a port forwarding rule to the IP address of your remote PC and use 3390 as the port, lastly when you connect to your PC, be sure to type in your remote routers WAN interface IP address plus a colon and then the port number i.e. 160.34.233.98:3390 in your Remote Desktop Connection window.
We have yet a third method for connecting remotely. LogMeIn is all web based except for the client you have to install on your remote PC. Basically you go to logmein.com and create a free account. You can have up to 1 remote connection for free which is really cool. The connection is all encrypted, and also will use windows pass through authentication instead of prompting you for more than one password. You can create your free account at http://www.logmein.com/.
All three flavors of remote desktop administration are really good. I tend to go with the built in XP Remote Desktop Connection because it is already built in, but the other 2 alternatives are definitely worth a try.