Wine:
   buffer_desc.ByteWidth      = sizeof(vert_data);
    buffer_desc.Usage          = D3D10_USAGE_DYNAMIC;
    buffer_desc.BindFlags      = D3D10_BIND_VERTEX_BUFFER;
    buffer_desc.CPUAccessFlags = D3D10_CPU_ACCESS_WRITE;
    buffer_desc.MiscFlags      = 0;
    ID3D10Device_CreateBuffer(device, &buffer_desc, NULL, &vert_buffer);

    ID3D10Buffer_Map(vert_buffer, D3D10_MAP_WRITE, 0, (void **)&vbuffer);
    memcpy(vbuffer, &vert_data, sizeof(vert_data));
    ID3D10Buffer_Unmap(vert_buffer);
Works fine.

Windows:
    buffer_desc.ByteWidth      = sizeof(vert_data);
    buffer_desc.Usage          = D3D10_USAGE_DYNAMIC;
    buffer_desc.BindFlags      = D3D10_BIND_VERTEX_BUFFER;
    buffer_desc.CPUAccessFlags = D3D10_CPU_ACCESS_WRITE;
    buffer_desc.MiscFlags      = 0;
    device->CreateBuffer(&buffer_desc, NULL, &g_pVertexBuffer);

    g_pVertexBuffer->Map(D3D10_MAP_WRITE, 0, &vbuffer);
    memcpy(vbuffer, &vert_data, sizeof(struct vertex_data) * 3);
    g_pVertexBuffer->Unmap();
Fails. Needs D3D10_MAP_WRITE_DISCARD.