I am currently creating a terrain mesh from a heightmap and putting it into an indexed triangle list. The problem however occurs when I render the primitives I end up with flashing cracks, that appear as thin lines, at the base of hills from a long distance away. This however does not happen on my friend's computer. The cracks disappear if I set my RenderState.CullMode to Cull.None. Any advice about how to fix this problem?

I think my brother gets the same problem or similar when he runs my program on his computer but I don't get it on mine.

Will have to check if culling resolves it for him but other than that all I can think of is graphics card differences.