The FATF and the OECD are separate organisations. Although the member countries overlap to a large degree, there are several countries which are members of the FATF and not the OECD, and vice versa. However, the FATF Secretariat (currently 17 people) is housed administratively at the OECD.
In addition, the FATF has not been formed as a formal international organisation. Rather, the FATF is a task force composed of member governments who agree to fund the FATF on temporary basis with specific goals and projects (a "mandate"). The most recent mandatewas approved authorised the FATF to continue to function until December 2012.