If you are looking to configure the claims based enterprise portal with Azure ACS you might find these sequence of posts worth working through as there is a reasonable amount of fiddly parameters to configure and new concepts to understand. Here is the sequence of posts to work through.
Part 0 – Setting up claims based portal sites.
This part covers a few concepts and some functional background behind what you will be doing.
Part 1 – Setting up the public anonymous portal site
This part covers the initial creation of the anonymous portal site.
Part 2 – Enabling Anonymous guest access to the public site
This part covers the local authentication settings that you need to configure to allow anonymous user and the guest user to login.
Part 3 – Creating the Azure ACS Namespace
This parts walks through creating the Azure ACS namespace and connecting it to your public site.
Part 4 – Configure the identity handling in the public site
This parts walk through the handling of the identification information sent back from Azure ACS.
Part 5 – Azure Login page setup
This part covers the configuration of the Azure ACS site and the public site to handle the login what will be used in the authentication step.
Part 6 – Create and Sing onto the Private Portal
This part is the last step which covers the hand over from the public site to the private site.
At the end of this sequence then you will have and environment that you can use to accept claims based logins either via the vendor portal or the customer portal or what ever functional you want to display via the security roles you assign to the user.