XP File Sharing with other OS

I have 3 computers with XP, ME and 98 on them. They are all using a combination wireless/line router to acess the internet. As well as local file sharing. Internet access is fine but while the XP computer is on the other computers cannot see each other (they are not listed in network neighbourhood). When it is turned off the computers can see each other again.

Thank-you for any suggestions.