Windows 98 clients lost connection with Server 2003

Hello!!.
I am having the following problem: I just have an installed network whose
server is a Windows 2003 (with all the SP's) and the clients are Windows 98.
The server Windows 2003 is DC and has a DHCP giving directions IP.
I have switch linksys SRW248g4 and the wiring is category 6 (certified)
During the day, at random moments, the computers leave the network (they
lose connection with the server) and must reinitiate them so that they can
return to see it.
Until now test without results:
- To change network cards
- To change patchcords
- To look for (in Internet) similar problems with he himself Switch (not
encontre nothing)
- To look for (in Internet) similar problems with Windows 2003 (not encontre
nothing)
- To assign IPs static to the clients

The truth is that I am disoriented, that not to look for more to solve this.
That it can be happening?
To somebody it happened to him?

Greetings and from already very many thanks!

Guille
Buenos Aires,
Argentina