In order to get SOAP up and running you will need to add a web services user in the admin panel.

First add a role for the user. (Roles are used to limit the permissions of the user)
• System->Web Services->Roles->Add new role
• Give the role a name
• Set permissions for the role
• Then create the user with these permissions
  • System->Web Services->Users->Add new user
  • Add information about the user (the API key is the password used for SOAP)
  • Under roles bind the user with the previously created role