Configuring single sign-on on MOSS 2007 can be a problem sometimes. Even you log in with an administrator account, when you want to create the SSO database at the "Manage Server Settings" page at "Manage settings for single sign-on" link, you can get a "You do not have the rights to perform this operation" error.
The solution to this problem is to give the same service account of SSO service as the SSO Administrator Account at the "Manage Server Settings" page, but if you do so, you have to log in to the Central Administration site with the SSO service account to configure SSO :( Sorry :(