2 possible ways off the top of my head:
way 1:
event:
every <length of the song> seconds of game-time
action:
sound - play <the song>
way 2: (jass - copy and paste)
function Trig_Create_Music_List_Actions takes nothing returns nothing
call TriggerSleepAction( 1.00 )
call PlayMusicBJ( "[pathname of song in here]" )
endfunction
//===========================================================================
function InitTrig_Create_Music_List takes nothing returns nothing
set gg_trg_Create_Music_List = CreateTrigger( )
call TriggerAddAction( gg_trg_Create_Music_List, function Trig_Create_Music_List_Actions )
endfunction