I have an active customer db, and an inactive customers db; they are almost identical, and should be, but are not always because I change the layout in the active db, and forget to change it in the inactive db.

Can I, and how, export a layout from one db and import it into the other?

I am using FM7 on a Mac.

Many thanks!

You don't import/export, you go into Layout mode and copy/paste. It is critical that the table occurrences (TOs) on the graphs be named exactly the same (which you can do, 'cause they're separate files), and the field names also. If so, everything should line up. But check carefully afterwards. It is, IMHO, easier to change a TO name (even temporarily), than it is to reassign a whole bunch of fields 'cause they didn't line up (it depends how many fields).

sorry but I am a novice; what is a table occurence, and how does one change them? I was able to paste the layout into the inactive db, but when switched to browse mode, I got lots of "table missing" messages.

Yikes. A table occurrence (TO) is one of the objects on the Relationship Graph. You can think of it as an "alias" of a table, in that it refers directly back to its parent table, but there can be several table occurrences of one table. If you've used earlier versions of FileMaker you may think of it as a "relationship," but it is more than that. The "relationship" is more the line between two TOs, with its little white box telling you what fields and operators are involved.

I've always found it hard to explain the concept...

A Table Occurance is a context based "view" into a table.

Its actually really hard to explain, see if this diagram helps. (note that the layouts are your point of origin for "views" into tables)

You may also want to check out David Kachel's whitepaper.

http://www.foundationdbs.com/downloads.html

and this PDF on key concepts.

http://www.digfm.org/ref/FM7_key_concepts.pdf