Will fs2004 add-on's from a c-d and INTERNET be compatible with FSX?
From Microsoft's website:
Q: Will aircraft from FS2004 be compatible with “Flight Simulator X”?
A: Backward compatibly with existing 3rd party content is and has always been a priority for us, and we attempt to test as many add-ons as possible in order to provide the greatest level of compatibility.
Some are and some aren't. Those that will work in FSX don't look quite the same as they did in FS9 due to some graphics-related stuff I haven't gotten my head around yet.
Also, none of the FS9 a/c have the small image that appears in the a/c list in FSX.
Most likely not, FSX file system is much different from FS9, but thankfully most companies will be able to patch there products over quite easily.