Dear sky warrior
I was in the same situation few months back I am long time modeler (35 years!) and mac (15 years) mainly for your reasons I brought a PC P4 2.4 GHz 556 Ram fast 80 G HD NIVIDA GeForce FX 5200 with ACER AL922 19!QUOT! TFT (suitable for Mac too). Work fine with Realflight G2 with all 3D feature on Home XP. Still use my Mac G4 800 Mhz with apple 17!QUOT! TFT display for almost every thing else. I set up home network for transferring files from mac to PC (MS office Hebrew enable works only on windows). I do not think you can share your i Mac monitor with a PC because it is integral part of the system as in laptop. you may be able to use your PC monitor on the i Mac as a second display. As for Sim I think the both reflex and Aero fly pro are better for 3D type models and their malefactors are more familiar with your transmitter than realflight.
i wish some one will offer model airplane Sim for the Mac - Wolfgang, any comments?
Nahum