If you do a whois lookup (OS X's network utility lets you do this, or you can google for a web-interface), you might be able to get some contact information you can use to get in touch with the domain-owner.
Usually if the domain is for-sale it will have a page allowing you to buy it or make an offer or whatever though, your chances of getting it from the current owner are quite slim. If they're holding it maliciously, i.e - to stop you getting it and hoping to sell it to you for an extortionate price, then you can have it seized from them via ICANN's dispute resolution system, but it'd have to be a fairly solid case of infringement on a trademark or something.