A waste of time (Screen coordinates to world coordinates)

Today I wasted some time by doing this simple task.
I was following this article:

http://www.mvps.org/directx/articles/rayproj.htm

There are several odd things here:

void calcRay(int x,int y,D3DVECTOR &p1,D3DVECTOR &p2)
{
 float dx,dy;
 D3DMATRIX invMatrix,viewMatrix;

 dx=tanf(FOV*0.5f)*(x/WIDTH_DIV_2-1.0f)/ASPECT;
 dy=tanf(FOV*0.5f)*(1.0f-y/HEIGHT_DIV_2);
 lpDevice->GetTransform(D3DTRANSFORMSTATE_VIEW,&viewMatrix);
 D3DMath_MatrixInvert(invMatrix,viewMatrix);
 p1=D3DVECTOR(dx*NEAR,dy*NEAR,NEAR);
 p2=D3DVECTOR(dx*FAR,dy*FAR,FAR);
 D3DMath_VectorMatrixMultiply(p1,p1,invMatrix);
 D3DMath_VectorMatrixMultiply(p2,p2,invMatrix);
}

Basically it's about the tanf and the ASPECT division:

It's supposed I want to get a value between 0..1 in dx and dy, but tanf was messing the stuff...
I think the aspect is assuming the width is bigger than height, which is not my case, since I am developing for mobile phones...

Well, now it's working so it's time to relax... :D