Invalid home with instant client

My configuration:

Windows XP Pro
Instant client win32 11.2.0.1.0
Toad 9.7.2.5
Instant Client installation directory in PATH
tnsnames.ora and sqlnet.ora in TNS_ADMIN path.
No Oracle Client or any other Oracle software installed on the machine.

I cannot make the configuration above work. Toad home list shows the Instant Client directory in red and the message “This Oracle home is invalid”.

Is this configuration supported? Do I need to install the Oracle Client software? (it is not necessary with Oracle SQLDeveloper)

Regards

Juan Algaba Colera