Surface Transparency problem

It's been a while since I worked on this code so I don't have specific code to point at. I'm hoping someone else has run into this situation also and can point me in the right direction.

I have game code I am working on.
I use a height map user for land terrain for a water based game with some islands.
I use a flat terrain for the water which is partially transparent so that the land terrain features are some what visable.

The result is nice however, some video cards seem to not display it properly.
Ex - My desktop PC works fine. On my laptop the water terrain flickers on and off.

Pointers?

ZBuffer probably, if you're using a 2D plane for you water I've found it's a good idea to position the plane directly under the camera, or there abouts and scroll the texture about on the plane based on the camera position.

Okay thanks for the pointer I'll look into it.
That could get complicated as I use an animated texture for the wave effect.

Nah, doesn't make any difference, you just use positiontexture, you've just got to take into account the texture scaling with your x,z world co-ords.