i think to make it easier i just need to select meta_key and meta_value that have the same post_id. so if the user searches for dvd = 'animation' and book = 'php book' it will return no results because they don't share the same post_id.
if the user search for dvd = 'action' and book = 'mysql book' in that case it would return both values, because they share the same post_id.
i hope i explained it better, it much more difficult to me to explain it in english.
edited: @r937 just saw your query, gonna try it now.