It was a struggle. Here’s the shortcut:

1. Download the IBM Informix Client SDK3.50 – I used version 3.50.FC8 – for operating system Windows (64bit).
I found that the Infomix Connect 2.90 (choose the 64 bit option) also works – but you’ll have to run it as Administrator on Windows 7.

2. Edit c:/Windows/System32/drivers/etc/services and add

sqlexec 1526/tcp #

on the last line. Note the hash(#) at the end of the line.

3. Edit c:/Windows/System32/drivers/etc/hosts and add

(your Informix server IP) (your Informix server name)  e.g

12.345.67.89      informixserver.com     #

on the last line.  Again, note the hash(#) at the end of the line.

NB:  Make sure you define your host (e.g informixserver.com) in SetNet32!  (part of IBM SDK install)

Note:  If Windows 7 complain that you you’re not allowed to save or make changes to the file ‘services’ or ‘hosts’ – try opening Notepad as Administartor (Swift + Right-click) – or even copy the contents of the (say) hosts, rename the old file (hosts_old) and past into a new file (hosts).

4. Create a file (say) your_data_source.dsn in C:/Users/YourMachine/AppData/Roaming/Microsoft/Queries with contents

[ODBC]
DRIVER={IBM INFORMIX ODBC DRIVER}
DATABASE=your_informix_database
HOST=informixserver.com
SRVR=your_server
SERV=sqlexec
PRO=olsoctcp
CLOC=en.US.CP1252
DLOC=en_US.819

Note the ‘informixserver.com’ host as specified in point 3 – and Setnet32 – above!

OR

Go Start > Control Panel > Adminstrative Tools > Data Sources (ODBC)  to add a User DSN or System DSN  (both work).  Or access via C:\Windows\SysWOW64\odbcad32.exe

5. Now the datasource should appear in MSQuery!