The new sbs has dhcp and dns and this is turned off on the old server.
The problem is that when the clients are working on files on the old server (typically word-files) the normal and auto-save is extremely slow - sometimes even the connection to the server gets lost entirely. When this happened I tested trying to open up shares by Start - Run - \\sharename and it timed out. Pinging the server didnt work either. Accessing wan worked just fine.