Laser,
I'm not entirely sure I know what you mean. To select the Concorde for example, you go to 'create a flight' then to the 'selected aircraft' menu, pull down the menu until you see 'Aerospatiale/BAC' and select 'Concorde' in whichever livery you want.
For the PMDG it's the same method but underneath the default 'Boeing' in the menu you'll see 'Boeing PMDG' and then go in there and select the model of 737 that you want, 600/700/800/900, in the livery you want.
For ATC services, load up a flight with the planner, once your 737 is loaded up ask ATC for your IFR clearance, and away you go!
And Kestrel, I know what you mean!