Finally I got it working on Windows NT workstation/Windows 95: I had to reformat the machine, reinstall NT, then Oracle8i client.

Now I am using Microsoft ODBC for Oracle (MSORCL32.DLL, version 2.573.4403.00) with Oracle8i client (8.1.6) and connecting to Oracle7/8/8i(8.1.6) databases. Happy end.

Thanks for your help, guys.