Wow. I don't know what XP network setup is like, but some common mistakes I think happen in any windows system. Make sure all computers on the network have at least one Network Service and Network Protocol in common (use the network icon in the win98 control panel). Most commonly, NetBEUI and TCP/IP are setup on all computers, and each application selects the one it likes.
If a computer shows up on the network, but it's drives aren't available, and it's at least in win95/98, you must manually turn on 'sharing.' Open "My Computer" and right click on each drive icon, then select 'sharing.' If it's a home network with trust all around, just set all drives to Shared as...full. When you're through, a little hand should be show reaching out to each drive icon within 'my computer.'
It finally works! I did have to set up the file sharing on the old computer....once I get the old files off, I don't really want my son & his friends messing with them, so I don't think they are gonna get full access to MY computer! :)