unplayable files (movies mostly!)

[nibora]

i'm tired of downloading a movie of +/- 700mb's and then when i open it, i'm told to go to this site because the content is blocked (or somesuch nonsense)
is there a way to filter or somehow 'tag' these files so those who have these mysterious codecs (that don't seem to appear for me since the sites seem to be bogus, but another day another problem!) can access them and those of us w/out can avoid them and not waste time and harddrive space downloading them? maybe it's me and my (beloved mac) machine but... this is getting very frustrating and i log on less and less.
thanks!