The laws really depend on where you are located in the world. If you are in the United States, your two references should be the RIAA (Recording Industry Associateion of America) and the DMCA (Digital Millenium Copyright Act of 2000). If you live elsewhere a simply Yahoo or Google search for ''copyright laws'' (I think part of the problem you were having is the spelling...it's copyright, not copywrite) along with the name of the country/territory you live in.
In short, if you live in the US, you cannot provide a download of a copyrighted song, period, unless special permission has been given by the artist/music studio. Having the song simply play on your sight, with security measures in place to make sure someone cannot download the song, is an issue I'm not sure about, so I suggest checking the documentation provided.
Finally, no matter what country you live in, you should put a disclaimer on your site. If in your country you are allowed to offer the music for download, note that it may not be legal to do so in all countries, though it is in yours, and that website visitors should check their own local laws before proceeding. If you are simply playing the music on your site, and not offering it for download, state so, and why. Finally, remember that if you choose to stream music and not offer it for download, someone could read your source code, find out the location of the music file, and use that to download. Thus, you'll want to look into how to protect the content on your site.
Hope this helps,
John