i've attached a local .flv video to my post (it was uploaded and is inside my mediapool). my question: how can i display it inside my post? (the video player)
The .flv is not a video player in itself, rather just a video file to be played in one.
To display it, you'll need to play it from an actual video player. Unlike .wmv and .mp4, .flv files won't play natively in your browser without one.
take a look at:
Its a plugin that will take care of all your media needs including an flv player
(long name for a plugin).