Hmmmm,

The CD key isn't actually on the CD, it is generated and stored on your computer somewhere in the game files on your PC.

I have no idea how this is done but it may use some information that is on that particular PC in the process. The implication of this is that migration of the generated key to another machine would not work.

muert0 has the best solution in my opinion. It really isn't worth the risk with an online game.

Just my £0.02