Trouble is, as a complete novice, I have no idea how to add/install the DITA DTDs/schemas to <oXygen/> to enable interactive validation. A Google search was fruitless. You would be amazed how many web pages have the words "install" [or variations thereof], "oXygen" and "DITA" on them but don't actually tell you how to do it!
So if someone has done this or can point me to a web page with the information I need, I would be very grateful -- and probably not the only one on this list! Just remember, I am a novice

Regards,
Hedley