OK so you have a UNIX host that works.....
check what permissions are granted for that user id, especially the hostname... it could be % or it could be a specified IP address, IP range or hostname.
you could chjeck the userid on the unix command line, or use the Linux version of Administrator or Query Browser.. if its not installed on the Linux Box, it may well be on the installation CD.
What type of DSN are you defining?
does the DSN pass the tests
One of the advantages of downloading Administrator onto you box is you cna proove the connection, so there are fewer issues to resolve.