Vector4 p[6];
Matrix4 matWorld;
Matrix4 matView;
Matrix4 matProj;
Matrix4 z;
pDevice->GetTransform(D3DTS_WORLD,(struct D3DXMATRIX *)&matWorld);
pDevice->GetTransform(D3DTS_VIEW,(struct D3DXMATRIX *)&matView);
pDevice->GetTransform(D3DTS_PROJECTION,(struct D3DXMATRIX *)&matProj);	
z=matWorld*matView*matProj;
z.Invert();
//Plane equation: ax+by+cz+d>0
p[0]=z.Transform(Vector4(0.0f,0.0f,1.0f,0.0f)); 	//Front:	z>0
p[1]=z.Transform(Vector4(0.0f,0.0f,-1.0f,1.0f)); 	//Back:		z<1
p[2]=z.Transform(Vector4(1.0f,0.0f,0.0f,1.0f)); 	//Left:		x>-1
p[3]=z.Transform(Vector4(-1.0f,0.0f,0.0f,1.0f)); 	//Right:	x<1
p[4]=z.Transform(Vector4(0.0f,-1.0f,0.0f,1.0f)); 	//Top:		y<1
p[5]=z.Transform(Vector4(0.0f,1.0f,0.0f,1.0f)); 	//Bottom:	y>-1
[/SOURCE]