win98/winxp networking problems

I have a win98 PC and a winxp PC. I recently purchased a linksys router and
have connected the two together in a network. The winxp is the ICS. From
the winxp, i have acess to the internet, e-mail, and all drives on the win98.
From the win98, I have e-mail and internet access but I cannot look at winxp
files or computer. It can't find the winxp computer. Because of the
internet, I know information is travelling through the ethernet cable to the
win98. The network setup wizards say everything is fine. Workgroup names
are common. Any help or assistance would be appreciated.

By the way, it says my IP address will be included in the header. Is this a
security threat. Do I need to change anything to protect myself once my IP
address is out there?

Thanks for helping,
Mike (stumped in network land)