Microsoft users know of a great tool called "Remote Desktop" which allows a user sitting at home to control another computer at some "remote location". You get to see the entire desktop, issue keyboard level commands, move the mouse - just like if you were sitting in front of that computer.
Ubuntu is no different. In fact, you can control either a Linux based machine or a Windows based machine from Ubuntu. You only need to have network access to the computer you want to control which can either be via your local area network or over the internet. You also need to know the "host name" or the IP address of the computer you are connecting to. Google around and you'll find tons of articles on static IP addresses, remote desktop, remote control, DyneDNS, etc...the tools of remote connections.
So, assuming you know all this, just open a terminal in Ubuntu and type "rdesktop" followed by either the hostname of the remote computer or its IP address. Something like this, "rdesktop 192.168.1.105" for a local area network connection" or "rdesktop my.computer-at-work.com" for an internet connection. You can make the remote desktop screen completely fill the screen on your monitor by adding "f" in the command line text like this "rdesktop -f 192.168.2.105" where the "-f" means "full screen".
Give this a try. You'll be impressed.