Asking first is a pretty good policy, I think. If someone changes their mind, all they have to do is say so, here or in the comments, and as long as I or the person who posted it in here find out about it, we can remove the post without any hassle.
A good format would probably just be putting it in BBCode quotes and listing the commenter's name, like:
[ quote=Name] [/quote ]
But feel free to use whatever format you want, as long as credit's given where it's due.