Accessing computer with W98

I have a desk top computer running windows 98, a lap top
with XP, I have set up a wireless router that is connected
to the desk top. I have no problem accessing the internet
from both computers, and can access files on my lap top
from the desk top. However when I try to access my desk
top I get a message that I do not have permission to
access the computer and to contact the network
administrator. I know it is in the settings on the desk
top but do not know how to coeect. Any help will be
greatly appriciated