Just a couple of ideas.
What is the path on the current NT server? If it's \server_name\user_name, then you can use the cifs.home_dir option to make the filer automagically make that share work for everyone.
If it is some other path like \server_name\Users\user, then you can create a share called 'user' just like on your NT server.
OR, if you don't want to alter the server_name part and you can take that NT server name out of production, you can make the name of the NT server a NETBIOS alias on the filer (look under options cifs, you'll find it) and then the filer will answer for the old server name as well as it's own. But again, this means that your old NT box will have to go out of production or have its name changed.
Just a few ideas..hope this helps.
-- Adam Fox NetApp Professional Services, NC adamfox@netapp.com