Beginner problem with quads

Hello everyone.

I’m a beginner and this might be a simple problem, so bare with me.

When I render my F117, I get ugly lines running across quads as if they were triangles - like this.
This is the wireframe and the solid. All the faces are quadrilateral.
Can anyone help? Thank you.

PS: Sorry, couldn’t post images for some reason, had to link.

Set shading to smooth, think that is your problem. (press T in object mode, then click smooth).

I’m using 2.49. When I press T it brings up a ‘‘texture space’’ menu. I tried selecting individual faces and setting smooth, but some black streaks appear beside the faces’ edges.

The faces are non planar so the renderer shows as 2 triangles. To set an individual face as smooth select it and use W / Set Smooth.
If you are getting black edges try selecting all the vertices and recalculate your face normals with Ctrl+N

Thanks. I tried what you said, and it does work. However, how do you smooth out faces without making the edge between them becoming undistinguishable? I tried creasing and it doesn’t work.

Set your whole object as smooth then add an Edge Split modifier. Adjust the angle value and see the effect in the 3d view. For more control deselect the angle setting and select the edges you want to be sharp, then Ctrl+E / Mark Sharp.
http://wiki.blender.org/index.php/Doc:Manual/Modifiers/Mesh/EdgeSplit

Thank you.