I'm a newbie to Centova/AutoDJ , just migrated from the sinking Radionomy. I'm wanting to set up a timeslot where music from a particular playlist is broadcast along with specific imaging/jingles.  I've got so far as setting up a playlist of music files in a Scheduled playlist, but cant work out how to schedule a certain set of jingles only to playout other than to add them into the same playlist as the music files.  Is there a way of doing this ?

Sorry in advance if this is a stupid question !

You'd want to create an Interval playlist type for your jingles. However, Interval playlists will never play over your Scheduled playlists, only over General Rotation playlists.

So you would want General Rotation playlists to handle most of your music, and Scheduled playlists only when you want to schedule a shown or event (jingles from Interval playlists won't work here, so you need to include jingles within the Scheduled playlist itself)

You can read more about how playlists works here:
http://www.centova.com/doc/cast/user_manual/02_reference_manual/12_playlist

So would it be possible in any way to set-up a 'slot' that ,for example, plays just 90s music from a playlist, with 90s show jingles, other than setting up a Scheduled playlist that contains music & jingle files set to play sequentially ?

You could arrange your daily music schedule into General Rotation playlists. Something like
00:00 - 06:00 Various
06:00 - 12:00 Morning music
12:00 - 14:00 The '80s
14:00 - 00:00 The '90s

But make sure to also have one General Rotation set for the entire day, as a fallback, otherwise Centova Cast will ignore the time restrictions on your other playlists. So have one like:
00:00 - 00:00 Fallback

It could even be composed from a single track which contains like a second of silence, or from a bunch of tracks that you don't mind if they rarely play during the day. Set this playlist to have the lowest weight (1), as tracks from this playlists will still pop from time to time. With a low weight this will happen very rarely.