For help on hash tables obviously the best place to start is the mIRC help file - type /help hash tables
There is also a tutorial written by KingTomato about hash tables here
. There is also an older one here
(written by Ophidian) which, judging from the description, was written back in the times of mIRC v5.8 when hash tables were introduced. Due to this it may be wiser to use the former first.
It would be an effective way of storing a long list of mp3s.