For each IIS action, you can specify the IIS Server as either a global server (specified in the options) or a particular server name. You can also specify credentials as either the credentials specified in the Options, or a particular set of credentials.
If the credentials are left blank, Windows authentication with the credentials of the currently logged-in user will be used.
The IIS 6 Actions use WMI to connect to the remote system, so you will need to ensure that WMI Remote Administration is available on the host computer. Here is an MSDN article about configuring Windows Firewall for WMI.
To select the global server name and credentials, choose Options from the Tools menu and then click on the IIS 6 Options tab under 'Internet':