This line is using the deprecated pass-by-reference:

    $block['content'] = zillow_form($form, &$zinfo);

You can fix that with no anpersand:

    $block['content'] = zillow_form($form, $zinfo);

And I think your submit function should be named zillow_form_submit instead of zillow_submit_info.

This line is using the deprecated pass-by-reference:

    $block['content'] = zillow_form($form, &$zinfo);

You can fix that with no ampersand:

    $block['content'] = zillow_form($form, $zinfo);

And I think your submit function should be named zillow_form_submit instead of zillow_submit_info.