I also use logmein, but agree that having UVNC works well internally so that you do not have to connect out to connect back in initially.
As for your setup, you are looking at having the Win7 Laptop as your server (the one which you will authenticate to in order to view) and your XP Desktop as your viewer (the one you will be viewing another machine from.
*Note: Install the Server and Viewer on Both if you would like to be able to connect to each other from each other.
In your case, to set up Win7 Laptop as the server (to be viewed) you can follow that URL you gave and then launch the viewer software from your XP Desktop. Enter the hostname (if your internal dns works well) or the IP of the Win7 Laptop into the Viewer software on your XP Desktop and connect that way. This will establish a connection from the XP Desktop to view the Win7 Laptop.
