Internet connection sharing between Win 2000 & XP home

Hello eveyone! This is driving me f**king mad. I have a desktop PC running windows 2000 professional with a broadband connection to the net which works. I also have a laptop running XP home networked to my desktop pc using a networkcard and ethernet cable. both computers can talk to each other and access shared file, but I cannot get the laptop to share the desktop Internet connection. I have followed about 5 different tutorials from the internet but none of them work. I bet my life on it that the desktop is set up correctly but there is a little niggle that it is probably the laptop which is the problem, or it soon won't be when it gets thrown out the window!! only joking. I have had the home XP laptop sharing a connection through a desktop running windows ME before so I know it works. PLEASE PLEASE can any one help me???