Playing MP3s

I really like to know how can you play MP3s (like the Halflife songs) in the game? Do I have to use the Ambient Generic entity?

Yes, you play sounds with the ambient_generic, as for playing music off
the CD, there was a entity alone that did that, cant remember what it
was in HL1, nor can I find it in the HL2 ents

Hmm... I did something like this:

Sound Name: music/hl2_intro.mp3

But no sound was played... what am I doing wrong?
Is it just the path that is wrong?

make a sound folder in your HL2 directory.

then make a folder in that called mp3 and put your song there.

now filter out mp3 in hammer and it will show up and play in your level.