If you have videos in flash format (.flv) or vid which is incomplete(unfinished/ incomplete download) you can open it with VLC MEDIA PLAYER.
It's good for previews too.
where do i get one of these vlc programs?
you can google VLC Media Player, or something like Riva. I use Riva and it works great for me.
EDIT: Check the various discussions, i have uploaded a copy of a Riva installer.
problem- i'm on a mac... i don't think it's mac compatable....