Network Neighborhood disapeared- help !!!

[Artur]

I have samba server 2.0.7 installed on Linux 2.2.17 and from times to
times computers in neighborhood
disapear without any notifications in log files. I have another network
with the similar configuration + NT proxy connected via ISDN modem to
Internet. The same things occure when
NT connects (dial in) Internet. The samba server with neighborhood just
vanishes. Samba server
does not work as PDC and simply shares just files and directories. What
could cause this behavior ?

Artur