Not able to Bonjour chat with macs on my network

I'm trying to set up a bonjour chat system with my office building. Most people are on Macs and are able to chat fine through iChat. However a few people are on windows machines, and I cann't get their chat to work properly.

They're using Pidgin on Windows XP professional edition 32-bit machines, with service pack 3 installed. I've already installed the Bonjour printer support application from apples website

When they open Pidgin and sign in under their Bonjour account, the people on Mac's can see them on the network, however they cannot see anyone, and if anyone tries to send them a message, it gets bounced back saying "iChat can't start the chat, the invitation to "persons name" could not be deliviered".

Their firewall is not active, so that shouldn't be blocking the chat. And their computers are networked fine... they can see all of the mac computers on our network.

Is there something that I'm missing? or something else that I can try?