i've seen on some boards where the text is put the same color as the background, dont know if its just changing the font color or what but it could work like current tags ie
[spoiler]This text will be hidden until highlighted[/spoiler]
that would show up on screen as
SPOILER - highlight to view
This text will be hidden until highlighted
END SPOILER
and the italicized text would be the background color so it doesnt show. the other way ive seen it is as a button (would say spoiler) so you need to click the button for the text to show.
i like the first way better as it is a) probably easier and b) would automatically be rehidden next time you enter the thread (so if its someone else)
-Darth Simon