nope, decompresses fine.
i also just reinstalled it from scratch, and it still has the issue.
Same here. I even deleted my old profile so it created a new one and the problem persisted.
However, playing around with the settings, I found what triggers the problem and how to work around it, but the workaround disables other things.
Namely, the problem is caused by the GLSL Shaders. Turn that off from the video options and the 3D Geoscape is visible. Unfortunately, turning the shaders off necessarily means turning off post-processing shader effects so you can't make the political borders visible. You can make the radar range circles visible with the shaders off, but it doesn't show the grayed out radar shadow areas outside detection range.
Interestingly enough, the political map makes the continents and islands visible even on a transparent map, so you can play, but terrain details are naturally missing. The view is pretty surreal. And very, very neon.
Hopefully this helps in pinpointing where the problem is.
I'm running Windows XP Pro SP3 with 4 GB RAM and an ATI HD4870 256MB graphics card.
My ATI drivers are not the very latest yet, but within half an hour they will be and I'll post the results then. I don't think that will do very much, however.