Does anyone know how to configure a transformer in mindi

I was wondering if anyone can help me with the problems I have with using the transformer in mindi 540 free edition. I can create this schematic https://www.hobby-elec.org/e_ckt7_2.htm of the astable multivibrator but which I can run without errors although I am recieving a flat voltage output instead of a square wave pulse but at least I'm running it. Whenever I add a transformer it wont run so what is it I need to do, there doesnt seem to be a facility for creating a centre tapped transformer. I'm having doubts that I can even simulate a DC to AC Inverter with this software.
Else does anyone know of suitable simulation software I could use.

I recommend LTSpice from Linear Technology. They have an active Yahoo group with some very smart guys to help you.