We have a smb share on our Netware 6.5 server that we successesfully
connect from OS X using AFP and SMB, but we can not connect from a
windows client (tried vista and xp) .... that do not have a netware
client installed.

On the windows client I get ...
net use w:\\ipaddress\volume

System error 53 occurred.
The network path was not found.

Any suggestions on what to try?