How to turn on Blogger access in your domain
Go to the Google Apps control panel, and sign in to the domain-management function.
Log in, using an account with domain administration rights.
Go to the Organization & Users tab
Switch to the Services sub-tab
Scroll down to the Other Google Services category
Note the Terms of Service issue described on the screen - only continue if this does not cause a problem for your company etc.
Find Blogger in the list (it's currently 2nd in my list, so easy to find).
Click the On button beside Blogger, so it goes green.
Click the Save changes button at the bottom of the list.
This will allow every user in your domain to use Blogger, by logging in to www.Blogger.com with the domain account that you set up for them.