[Samba] Can't ping samba box after a while

[Chris]

We've got Samba running on a CentOS box. The rest of the network is 
Windows, controlled by a Small Business Server (Windows 2003). The Samba 
box gets an IP using DHCP. The Windows 2003 server is the DHCP server.

When I reboot the samba box, I can ping it by name for a while. "ping 
myservername" works fine. After a few hours, though, I get "Ping request 
could not find host" errors. I can still ping the server using the IP 
address.

What could cause this? Is it a problem with my samba configuration, or 
with the Windows server?