You really need to have a separate "role/actor" Table, as June7 suggested. Your 'movie' Table should include all info on the film, except for the cast members, and should include a MovieID.
The movie Table would be used as the Recordset for a Main Form, and the role/actor Table (which also needs a MovieID field) for the Recordset for a SubForm. The Main Form/Subform would be related thru the MovieID.
Linq ;0)>
The problem with making anything foolproof...is that fools are so darn ingenious!
All posts/responses based on Access 2003/2007