And to ShaneG: How do I set the bufferpool entry lower?
If you didn't add the bufferpool entry from NickN's to the FSX.cfg then do not worry about it. If you did, follow his guide for the correct setting for your system.
A recent tweak of setting a high entry for the BP has caused this anomaly for some, including me.

After looking at your specs,
Does this problem occur with planes that used to work fine, or only with newer downloaded planes?
I ask because Boikat used to have a problem similar to this with his lower end graphics card, and I know Brett & Alrot's planes will not display correctly on low end vid cards as well.