Xp sharing folders in NT 4 environment

I have an office with a Toshiba Tecra 9100 running XP with no service packs. They are trying to share out a folder on the c drive and whenever an NT 4.0 machine in that LAN tries to map to the machine they receive a network path cannot be found message. The xp machine can map to an NT4.0 machine fine and I can map to it’s share from my machine here in corporate from the WAN. What do you think is the problem?