So you want to know how to make music codes eh? Okay well first off you need to find a place where you can upload your music.
I suggest fileden some of my friends use that. OR there is another way you can go. You can just search google for mp3 urls!
Okay now once you have found your MP3 url you must make sure is does not have any weird characters such as %*^ things like those. Most common urls have the "%" in them that is NOT acceptable for neopets filiters!
One of the two things will happen

1-A window will pop up saying only url ending in .mp3, .swif, etc. etc. are allowed
2- it just wont play when you vist the page where you added the code!

So that makes it a little harder to make music codes! But hey you can do it!
Once you have got a GOOD music code all you have to do is copy and paste the url into the code bellow where it says "MP3 url here!"

<bgsound src="MP3 URl" loop="infinite">

Places to get/upload mp3 urls
fileden
mailboxdrive
uploadmyspacemp3music

There are lots more than just those 3 sites!