graphics errors on terrain

I have graphics artifacts/errors on the terrain, and I'm fairly sure it isn't the textures I use (I get them with the textures included in the example app, too).

here's a screenshot showing the problem:

(in case it doesn't like the image tag:)
www.lemuria.org/T2/weirdground.jpg

any help appreciated...
(note: This is on a Linux system (2.4.18 kernel, NVidia Geforce2 graphics card with latest (2880) drivers.