Is there a way to make sure my 2005 Highlander Limited is an AWD or FWD?

The VIN number should be able to be brought up by the service department at a Toyota dealership, and it will show the options as originally configured as well as the status AWD or FWD.

FWD: Means that the power from the engine is applied to the front wheel only.  This normally requires the use of a transverse (sideways) mounted engine and CV Joints.
AWD: Means that the power is applied to all wheels simultaneously.  This would require that the engine somehow applies the power to the front wheels and the rear wheels.  This is normally done via a drive shaft.  This would be obvious when looking under the vehicle.  There would be a shaft running from the engine compartment area to the rear wheels.