there is a seperate picture for the plane. if the plane is called "supercub" and all the files are called "supercub" then the preview picture would be "supercub_prv" this picture has to be in jpeg format also. so if you realy want to have a preview. you have to take a screen shot by going into fms and pressing printscreen on the keyboard. then go to clipboard and the picture will be there. then copy and paste it into a picture editing program like paintshop pro and crop the picture to get the preview you want. then save it as a jpeg. name it
"planesname_prv" planes name is what all the other files for that plane are named. that should get you started. that is about all i can explain so you are on your own from there. if you put that picture in the model file then you should have a picture in that preview thing.
if you have any questions then just e-mail me at
mvogelman@hotmail.com
hope that helps