Need help

i have a little challenge. I run a small office where I have a collection of Window 98, ME, NT, XP and 2000 platforms.
I setup a small internet connection using a PC running XP (home edition) as the Internet Connection Sharing (ICS)that is all other computers on my LAN connect to the internet thru this XP computers.
I am able to configure PC running 98, ME and XP to connect to the internet byt could not connect PC running NT and 2000.
Can you help?