About the File Extension White List Form
Use this form to limit which types of files users are able to upload by whitelisting file extension by adding to or removing from the list of file extension types.
Vista enforces the restrictions at the upload type level, that is, you may allow a certain file extension for one type of upload but not allow it for another type of upload. Press F4 in the Upload Type field to select one of these:
For network security reasons, best practice is to not augment this list except for when and if a file type that is not on the list needs to be uploaded.