Thanks for your reply. It was the menu bar on the client side I wanted to tinker with. I wanted to put the link to return to the main web site on it; also I wanted to change the wording of "Support Center Home".
I must say I thought include\class.nav.php was for the support staff side of things, not the client screen. I'll have another peer at it.
The Actinic web site comprises a series of concentric layouts; in theory (i.e. in my dreams) I could drop the osTicket screens into what I know as my 'outer layout' (the stuff that produces the top, bottom and both sidebars), if I was able to transport and add all the includes etc. from osTicket to the Actinic outer templates, without any clashes or problems with paths.