mac os slow network performance issue

Hi i am here in a gigabit network with about 7 mac's with mac osx 10.6.8.

we have the strange situation that suddently unpredictable some mac's

are very slow in copying files from either a linux smb server or a windows 2008R2

server. after we noticed this, we can change the ip address of this mac and

then we have again normal fast perfromance. this can still work several weeks or

several days and then the game begins again -> mac is slow, i change the ip address

and everything is working fine ......what can this be ??????

this is happen to every mac, of course not at the same time but unpredictable which

mac has the problem.

thanks for any suggestions !

Hardy