Intellectual Property Rights
In the so-called real world, if you create something of value, then you have rights to help you try profit from your creation if you wish to do so. Second Life is no different. If you create something in Second Life, the you retain some basic rights to control your creation.
However, Second Life is not separate from real life, it is a part of it. The laws of the existing local authorities apply.
For example, if I sell some item in Second Life, and it is clearly marked that it is not copiable, and you make copies and resell them, then...well, then what?
Take the issue to your lawyer. Second Life is not responsible. They are like the phone company in this sense: they are usually not liable for illegal activity performed in SL, just as the phone company is not liable for crimes planned over the phone. Of course, like the phone company, they might be compelled to cooperate with various law enforcement officials to pursue law breakers.
On the other hand, Second Life does include an fairly elaborate technical mechanism to help with IP rights. For example, an item can be marked No Copy. This means that the simple methods of copying an item will fail. Remember that there is never a perfect technical solution. it is often still possible for a technically savvy person to copy an item, just as in the real world it is possible to take a photo of a work of art, frame it, and resell it.