Actually, if you email Noise Factory, they are going to tell you that they no longer sell internationally and that their international supplier is <a href="http://www.cocoebiz.com/" target="_blank">COCO Eboiz</a>. I bought the Metal Slug 3 OST from them and had absolutely no problems whatsoever.
As far as an AST, the OST is a higher quality mix of the game's OST (they recorded better quality then trimmed it down for the Neo) so it;s some high quality stuff. If you like the soundtrack in the game, I'm sure you'll love the CD.