Whoops, never mind, I got it to work. There wasn't any code, I just set up a varchar field in Enterprise Manager and pasted CASE WHEN TYPE='O' THEN ORGNAME ELSE LAST_NAME + ', ' + FIRST_NAME END in the Formula.

You can answer a question about computed fields, though. My understanding is that it should be a readonly field (ie, you never save anything to it), and it will automatically reflect any changes to the underlying columns (TYPE, ORGNAME, LAST_NAME, FIRST_NAME), right? It should basically act just like building the ....as CUSTNAME in a SELECT statement? I shouldn't need a Trigger.