Dragging out an AD component introduces a number of project properties to your flow. They should be populated with something akin to the following:

ADDomainAdminUser and ADDomainAdminPW should be self explanatory. As far as I know, you don't need to qualify the domain user with the domain i.e domain\user or in the format name@domain, but you may have to experiment if you're having problems.
ADDomainName should be a fully qualified domain name, like my.fakename.symantec.net
ADServer should be the IPAddress of the ADmachine
ADServerPort should be the default, 0, unless you've specified a different port.

Hope this helps.

To add to what reecardo said, you can set your AD connections/info at the project level so every AD component will use them rather than having to enter them form each component you drag onto the project.

In the project pane, click on the Name of your project (highest level), and click the properties tab, and you should see the fields that reecardo was referring to in the previous post.