Like da Rock has already alluded to I think your best bet would be to contact RealFlight Tech Support. As I understand it the G5 "Upgrade" has no effect on any prior versions of RealFlight that you may (or may not) already have on your computer. Again ... "as I understand it" the upgrade disc, once installed, utilizes the existing interlink controller so I would think that you'd be alright with getting just the G5 Upgrade disc. But, check with RealFlight first.