XP loses mappings to domain

New XP box with ALL updates as of today. Connected to W2K
domain controller through a d-link router. Domain
controller is running Active Dir.

Problem: When the XP box (a laptop) is idle for a while)
loses connectivity to the domain controller. Shows it in
Network, but cannot reconnect to any of the mapped shares.
Can still get internet, just no ability to connect to the
LAN per se.

Anyone have any ideas on what to check and where as far as
settings that would affect/control this?

Have to logo off and log back in to the domain in order to
refresh the connectivity right now.

THANKS!!