Connecting to Oracle Database with ODBC/Python
Are you installing the 32 bit drivers or the 64 bit drivers on Windows 7?  

I have to install the 32 bit drivers on all of our Windows 7 machines (even those running 64 bit).  

After that I have to set up ODBC using:   c:\windows\syswow64\odbcad32.exe  instead of through the control panel.

Your issue may very well be different.