You just have to add some assignments in client task manager over the group which they belong to it then drag and drop the found systems in that directory.
Now you can see the installation going to the rest systems you added.
Let me know if you got the right answer.
That won't work, I'm afraid: you can't use client tasks to install the agent, as they only apply to machines that already have an agent installed.
Abojama - I think what you're looking for is Active Directory Synchronisation. Please have a look at this section in the ePO Product Guide - in the 5.1 guide, it starts on page 99.