Roll back jQuery version to 1.2.x

Does anyone know how to rollback the installed jQuery version? I ran update recently and since then I've been having problems with numerous modules including: Lightbox2, pngfix, administration menu

I've seen various threads suggesting javascript is the problem so can only assume jQuery is the culprit

A site report doesn't reveal ANY jQuery version at all and I don't have the jQuery_update module installed

The most troubling problem is that when a user logs into the site via /user the attached image is the only thing to display in the browser window! (A refresh fixes this, but not all users will be that intuitive)