If you getting errors signing assemblies on Vista like below you might want to check some security permissions.

Cryptographic failure while signing assembly '....' Access is denied.

To remedy the problem I simply opened an Explorer window as an administrator and altered the ACLs on the necessary directory.  I granted my user Full Control on %ALLUSERSPROFILE%\Application Data\Microsoft\Crypto\RSA\MachineKeys.  Simply restart Visual Studio (if it was open) and you should be off and rolling.