Netowrking Win 98 and Windows Server 2003

My setup is this. I have 2 IP address, one goes to a
server (Windows Server 2003), and the other goes to a
router. The rest of the machines are behind a router. The
computers behind the Linksys router have mapped drives
(by IP address) to the server. The problem that I am
having is that my Windows 98 computers lose there
connection to the server withing the hour all the time
and they have to get rebooted to connect again. My
machines on XP connect fine.

The reason why the server is not behind the router is
because the router would time out one in a while and
people could not access the site hosted on the server.

Is there any ideas how I can get the Windows 98 machines
to stop losing there connection to the server. There are
no time limits or restriction setup on the user accounts.

Thanks