You will have to create a system dsn via Administrative Tools > Data Sources (ODBC) , odbc datasource on the windows system.
I have tested the same in Windows 2003, not sure @ the Windows 7. You can test it out further.
What Pradeep has mentioned is the right locaiton even for Windows 7
Control Panel -> Administrative Tools -> Data Sources (ODBC)
However if you are using 64 bit machine then you may not see Oracle for ODBC
in that case you have to manually execute C:\Windows\SysWOW64\odbcad32.exe file. Prior to that you may have to install ODAC 32 bit.