They should become activated if you open up a MaintenancePlan document window in SSMS.
to do that, do this:
1. connect to your server in Object Explorer
2. navigate to Management/Maintenance Plans
3. right click on the maint plans folder and select "New Maintenance Plan..."
4. this opens up the maint plan document window in SSMS, you can now drag tasks into the window.
Hope this helps!