Remote Desktop connection

I am having difficulty making a remote connection to my desktop PC running windows XPpro. I have a laptop running XPhome, which i network via 11 Mbps wireless network to the desktop. I want to control my desktop from my laptop accross the internet. Remote desktop was very succesful when the laptop was connected on the wireless network.

I assumed that the remote connection was over the internet since the laptop shares the broadband connection of the desktop. However, when i took the laptop to another location and tried to connect to the broadband assigned IP address (over the internet)of the desktop, the connection could not be made.

When travelling with the laptop I use a shared internet connection. ie I connect to the LAN (10 MBps) which has a broadband connection.