In order to get RealFlight Addon 1 and 2 to install, you'll need to pickup a patch file that RealFlight put out for these two addons... Here is a link outlining the problem and solution: http://www.gpsoftware.com/kb/q01-1036.htm

You don't have to sacrifce quality to get a higher frame rate... You should definately not downgrade the physics of the sim... Processing power on the physics will not affect the graphics in anyway... All physics are handled by the processor, and all graphics are handled by the video card... Your frame rate problem is probably due to the video card not being able to handle the rendering.... If you need to bump up your frame rate, remove unnecessary items from the screen. I usually fly at the Fun Fly field, but I take everything out except the runway, grass, distant trees and windsock... Everything else is just in the way and lowers the frame rate drastically... You can remove things by going to Airport, then select Item Visibility... if you click on ones with the checkmark, they will be removed from the view... You can easily add them back by clicking on it again. You can keep everything else like the visual details on high this way, everthing still looks good, there are just fewer things looking good with the exception of the aircraft...