A passkey is only necessary if you want to fold using the SMP client and obtain bonus points for early completion. To create a user name, all you have to do is pick one and enter it while configuring the client. Once you have completed at least one work unit, your user name will show up in Stanford's stats and you will be able to obtain a passkey.
[H]ard|DCer of the Month - February 2007/January 2
Joined
Sep 24, 2002
Messages
5,028
Go to This page and type in the name you want to use.
If it brings up no stats then your good to use it as your folding name.
If it does show any stats then somebody else has used that name and your best trying another name.