Model Question

What is it about some older models that make them not show in FSX?
Is it a file/texture issue, or because of the program used to make the model? Just wondering, I found a plane I've always wanted and was interested in what it might take to make it work in FSX.
If it can't be done, it's no worry, because she performs beautifully in FS9.
I was just curious about the reasons.
Thanks for any replies.
Is it a file/texture issue, or because of the program used to make the model? Just wondering, I found a plane I've always wanted and was interested in what it might take to make it work in FSX.
If it can't be done, it's no worry, because she performs beautifully in FS9.

Thanks for any replies.
