Networking XP system with 98 SE systems.

Here's a problem I've been having since day one. I had a 3 computer network with computer 1 running 98se, computer 2 98, and computer 3 98se. they are networked together with an 8 port linksys router. I added a new xp computer to the network and while the old computers still are able to share files the new one cannot. It's weird, but computer 2 sees the xp pc icon but reads it as it not being there. the xp computer can in fact take files from the straight 98 computer, but doesnt recognize any of the other computers. they all have the same workgroup name and the IPs are the same except the last number. How can I get file sharing between all 4 computers. I am also able to play network games just fine over all four. Also, are there any extra steps to take once I but broadband on the network so they can all share it? thanks for your time.