generate activation key for new users

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C#

Anyone knows how do we actually go about generating an activation key that a new user, who registers for an account online, to verify himself in C#, Visual Studios 2008 Professional?

We do not need it to be perfect, rather simple enough for a new user to finish up a registration form and receive the generated key email and use that key to verify himself before logging in as an user.

Is a Guid a good way of generating random keys?
Many thanks! ;)