I downloaded and installed the DREAMWINGSDESIGN Q-400, but it was impossible to trim.
Turns out, the empty weight was listed as 34 (yes, three four) pounds and the max at 64. Clearly the CG was about a mile in front of the plane. I could see no way to adjust the weights in FS9, but I am really new at this. Did I fail to do some simple thing? Apologies if this is covered somewhere, I looked hard. Any advice welcome! (I REALLY WANT to fly the 400)

For starters I am not familiar with the aircraft you talk about but I do know that all of the weights and balances for any aircraft are in the aircraft cfg file for each aircraft. You will find these files in each aircraft folder.
Below is the weight and balance for the default Mooney Bravo
[WEIGHT_AND_BALANCE]
max_gross_weight = 3368 // (pounds)
empty_weight = 2189 // (pounds)
reference_datum_position = 3.9, 0, 0 // (feet) distance from FlightSim Reference position: (1/4 chord, centerline, waterline)
empty_weight_CG_position = -3.7, 0, 0 // (feet) longitudinal, lateral, vertical distance from specified datum
max_number_of_stations = 50
station_load.0 = 170, -3.1, -1.5, 0.0 // Weight (lbs), longitudinal, lateral, vertical positions from datum (feet)
station_load.1 = 170, -3.1, 1.5, 0.0 // Weight (lbs), longitudinal, lateral, vertical positions from datum (feet)
station_load.2 = 100, -6.1, -1.5, 0.0 // Weight (lbs), longitudinal, lateral, vertical positions from datum (feet)
station_load.3 = 100, -6.1, 1.5, 0.0 // Weight (lbs), longitudinal, lateral, vertical positions from datum (feet)
station_load.4 = 33, -8.5, 0.0, 0.0 // Weight (lbs), longitudinal, lateral, vertical positions from datum (feet)
station_name.0 = "Pilot"
station_name.1 = "Front Passenger"
station_name.2 = "Rear Passenger"
station_name.3 = "Rear Passenger"
station_name.4 = "Baggage"
;Moments of Inertia
empty_weight_pitch_MOI = 2706
empty_weight_roll_MOI = 2131
empty_weight_yaw_MOI = 3932
empty_weight_coupled_MOI = 0.0