Andrew Connell has some good coverage on this issue in his book Sharepoint 2007 WCM Development. In the code downloads for his book he offers a control which suppresses the javascript files  as necessary for authorised and anonymous  users.

The code download is here, and Chapter 19 is what you need to reference;

www.wrox.com/.../...rver-2007.productCd-0470224754,descCd-DOWNLOAD.html


There's an article on the topic by a different author here;

msdn.microsoft.com/.../bb727371.aspx

If you're sold on the usefulness of Andrew Connells book it can be obtained here;

www.amazon.com/.../0470224754

It goes into much more depth than I can here (wouldn't be right to quote it verbatim!)