Pbarb2: You can't "delete" boards - but you can do what you said (change name of board to "." - so most will not find it.

To delete all messages, either click delete on all messages, Ask Fencer to do it for you, or probable the best - click "Edit" and change the read access to "Brain King" - that way not even you can see the messages in the board (so it looks like everything is gone)

Then just post in the description of the board "This board is closed." or something like that.