Rikard, The Uid class will give you an identifier that is unique on the machine you are using. If you need a true unique identifier, you can append the machine's IP.
There is an example of code for a distributable universal key generator at TSS here (including links to source code). Note that we used something similar on one of our projects, and I hated it. A lot. It's a very big solution to what may only be a reasonably small problem.