You should be able to just copy them over to the relevant folders (Depending on the type of addon, some more complicated ones will need to be re-installed from the installers). Did you backup the entire contents of your gauges, effects, simobjects etc. folders or just the addons within them?

With a defrag, you should do that after placing all your addons back into FSX, defrags make a big difference with performance!

And finally you will have to reactivate all your scenery libraries through the Scenery Library in FSX,

Hope this helps,

Matthew

I think it depends on the reason for doing the re-install. If you've had any problems at all it might be best to start from scratch & install the files again. This might be the best idea anyway. With complicated addons it's quite likely you would forget to back something up in which case they would never work properly.

1) Anisotropic filtering is the best, but needs more resources. Trilinear is second and bilinear is the lowest. If you are running FSX under Direct X 9 using an Nvidia card, you may aslo try using Nhancer to optimize your settings. There are some descriptions posted in the tweaks section here.

2) When you delete a scenery folder without removing the scenery entry from the scenery library, you will get this error message. There are 2 possibilities:
a) you know which scenery you have removed and can just re-install it again. Or if you know which scenery is causing the error you can remove it from the scenery library in FSX.
b) you can remove entry number 115 from your scenery.cfg. The location of the scenery.cfg can depend on the OS you are using. On my computer it is located under c:\Programm Data\Microsoft\FSX. It may be located in a hidde folder.