On what platform is IDS installed? On UNIX you can access the server with remote shell (from UNIX), secure shell and telnet (both from UNIX and Windows).
On Windows you could use telnet or secure shell but for both a server has to be installed (freeware) on the databasehost. For NT4 along with the IDS came the "Informix Enterprise" tool to be installed on the server or the client, for newer OS versions and UNIX of course the "Server Studio" tool is available.
If it's only the databases you want to approach on UNIX you can access them remotely with the dbaccess tool installed on the client but the simplest way I think would be through an ODBC (or JDBC) connection (both UNIX and Windows clients). ODBC and JDBC drivers are downloadable here:
http://www-306.ibm.com/software/data.../pubs/library/
Regards