Public folder not seen.

I work at a company where there are 9 computers networked (including mine). I can see and enter all the other computers, but my computer does not show up on the network. Everyone else is on either Windows 98 or XP. I am running on Windows 2000. No matter what we do, no one can see me. We have created a public folder (shared), we have looked every place we can think of to find a way around this. Can anyone think of a reason we are having such difficulty? I am on the network, can access the internet and have access to all other computers. We need to share an external harddrive, so this is very important. Thanks.