Can see clouds and some 3D elements through the plane

[Flashman]

Im having an issue with clouds and such being visible through the plane. The same is true of items such as tracers, the sight dimming glass and some other things. The main one is the clouds....

Really no idea where to start with this one.

GFX model settings are high, all others fairly low.

Comp specs: Win XP, ATI HD4870 (with latest drivers), Q6600 quad @ 3gig, 4 GB Ram.

Not sure if its a card issue (I dont think I had this before I updated my drivers, was running 10.3 drivers).

ANy ideas?