Ok... in love with these!
<heh heh heh> Now all we need is the HMS Enterprise <chuckle>
Here you go for a concept (not for me, I don't run sci-fi): The crew is trapped on the Holodeck in a program that is set to a late 1700's sailing ship. While having 1700's adventures they also need to figure out how to get out of the program.
I believe that there has already been an episode much like that in one of the earlier shows.
I know in one of the movies they started with a scene of the crew on the HMS Enterprise in period costume, but I didn't think they were trapped.