WINS Not working properly with XP Professional

Hello,
I am running Server 2003 with XP Clients. It seems to be
a common theme that from time to time the
network "disappears" from My Network Places, explorer,
and other programs and browsers. The domain is visible
but if you click on the domain name no other computers
appear. You can browse to the computers with the UNC
address or the ip address just can't see them in from
programs or browsers. Any Ideas? Maybe some setting I
have that is allowing WINS to time out or take a break?
I have my server set up as a WINS Server, DHCP Server,
and Domain Server with all machines pointing to it for
resolution. Resolution does occur and fairly quickly,
just not visibly.