Hi azurepancake.
Due to limitations within windows XP, when you remote desktop to the computer, it locks the physical user interface out, so that only the 1 person can change this.
However, you can use software, such as UltraVNC or TightVNC to do this. Googling either name will bring back a nice list of docuents and sets of instructions
When connecting from outside of your network, you need to get your IP address that your internet provider has provided you (
WhatIsMyIP.com - 64.118.92.20 is a good place), and connect to that from your office.
However, you will need to put a port forward on your router at home to the computer you would like to connect to. RDP uses port 3389 by default. VNC uses 5800 i believe - but i could be wrong.