// before I read in the heightmap and generate

// the vertex buffer

...
// when mapWidth is eg 4, the terrain is three squads wide

// when mapHeight is eg 4, the terrain is three squads tall

unsigned short indexCount = mapWidth * 2 * (mapHeight - 1);
WORD* inds = new WORD[indexCount];

int count = 0;
for (row = 0; row < mapHeight - 1; ++row)
{
  // I go over the rows like when lawning the grass.

  // On even rows I go from left to right and on odd rows

  // I go from the right to the left. This is done to make

  // all the strips being attached to each other

  if (row % 2 == 0)
  {
    for (int col = 0; col < mapWidth; ++col)
    {
      inds[count++] = row * mapWidth + col;
      inds[count++] = (row + 1) * mapWidth + col;
    }
  }
  else
  {
    for (int col = mapWidth - 1; col >= 0; --col)
    {
      inds[count++] = (row + 1) * mapWidth + col;
      inds[count++] = row * mapWidth + col;
    }
  }
}

// and here we create the index buffer

hRet = device->CreateIndexBuffer(sizeof(WORD) * indexCount, D3DUSAGE_WRITEONLY, D3DFMT_INDEX16, D3DPOOL_MANAGED, &ib);
if (FAILED(hRet)) return hRet;

// lock the buffer and copy the data

void *idata;
hRet = ib->Lock(0, 0, (BYTE**)&idata, D3DLOCK_NOSYSLOCK);
if (FAILED(hRet)) return hRet;
memcpy(idata, inds, sizeof(WORD) * indexCount);
ib->Unlock();

delete [] inds;
...