gibblyweeds,

This is easy once you get used to the somewhat round-about method and the oft confusing uses of the terms 'movie' and 'project': A movie is what you can see on the timeline -- a project can contain one or more movies.

First open your ceremony project and then, using 'File' >> 'Open project' open the reception. You should get a message asking whether you want to close the first one or 'add' to it. The addition doesnt put the reception onto the end of the ceremony, but rather gives you two independent movies in the one project. Note: at this stage you could burn a disc with two movies and set the action at the end of the first to be to continue on to the second. Handy setup if you want to jump to the reception only.

You can choose between movies available for editing using either the dropdown menu shown by a film reel icon at the left above the timelines, or from the list at the bottom of the main 'Window' menu entry at the top of the screen. I'd go to the the reception project and select all [Ctrl + A] and copy [Ctrl + C]. Then go to the ceremony project, make space for the play cursor at or a bit beyond the end, and paste with [Ctrl + V]. 

Now you've got everything as one movie, but you are not done yet! Though both parts are now on the one timeline as you wanted, the ceremony movie is still part of the current project. Delete it by selecting it and using 'File' >> 'Manage movies' >> 'Remove from project'. Lastly, even if you save your new (single movie) project as say 'Full Wedding', the movie it contains is still called 'Ceremony'. You can change the names of individual movies from either the 'File' >> 'Manage movies' menu or from the film reel icon dropdown menu.

Regards,

Carl