Basically, you are buying the "licenses" for using VSL products. And thusly, only one license can be put on one Vienna Key at a time. So, for example, if you had Chamber Strings, you can download that license on either YOUR key, or your brother's key.. but not both. Of course, you are (as far as i am aware) allowed to download the actual sample data on to any of your computers, and then move your key back and forth from your laptop, to your desktop, or whatever. But you will only be able to use it on ONE computer at a time. However, there may be some technical legalities on that since you are inquiring about using it with you AND another person, so don't quote me on that... i'll let the VSL staff chime in on that when they get to this thread.
But, in a nutshell, you are buying the license (i.e. the *right*) to use the VSL samples. Of course, you are always welcome to buy two (or more) vienna keys, and say put all your strings on one key, and all your woodwinds on another. But remember, the VSL libraries will only work on a key on which the accompanying licenses are present. So basically, NO, you cannot "copy" your license or double them up on a second USB key. Understand though, in VSL's defense, this is to protect their product. If copying the licenses from one Key to another were possible, pirating of the software would be too easy: someone could simply purchase multiple keys, install the sample data on numerous computers, and then the only money VSL would be getting would be for purchased USB sticks... and you could use several thousands of dollars worth of products by only ever purchasing a few $49 dollar Vienna Keys.
It is in their interest to do this to protect their product. I know it can seem frustrating to consumers sometimes, but considering how prolific pirating of software is these days, it is a sure fire way for them to ensure they arent getting ripped off.
Stephan, Paul, and the rest of the VSL staff are VERY GOOD at checking in on these forums, so im sure they will pop in here and clarify all the details of usage rights concerning their products.
And as a side note, i DO believe that some of the software products (such as Vienna Suite, Ensemble,) DO provide you with multiple licenses under the assumption of when you use master & slave computers. However, it does not apply to the actual instrument/sample libraries, jsut a few select software programs.
I'm sure they'll respond in here shortly... :) Best of luck!
-michael