Hardware and performance

I've set up our moodle to be available via 2 virtual web sites (Win2003, IIS 6). One site is accessed via an internal address using Windows Integrated Authentication (users don't need to login to moodle), which gives direct access to the server. The other is a public address accessed from outside, through our firewall - using Basic authentication for credentials (rather than moodle's own login). Config.php has been tweaked to keep addressing sensible, and login.php, auth/index.php to handle authentication.

However the problem is that if I "insert a label" and place an image in the label the address is stored in an absolute form constructed from the address being used to access moodle. If we then access moodle from the other address then the resource is not available.

(In fact if created internally and accessing externally it will be give the internal address, which is meaningless. If created externally and accessed internally then credentials are prompted for.)

Is there a way around this, or can moodle only properly be accessed via a single URL (I have found mention of this in the forums but with no conclusion).

Puzzled, Tim