I simply added the effect directly to the mat_grain material. My video card is a GeForce FX 5200.

Code:

---

material mat_grain
{
	ambient_blue  = 255;
	ambient_green = 255;
	ambient_red   = 255;

	diffuse_red   = 255;
	diffuse_green = 255;
	diffuse_blue  = 255;

	specular_blue  = 255;
	specular_green = 255;
	specular_red   = 255;

	emissive_blue  = 255;
	emissive_green = 255;
	emissive_red   = 255;

	albedo = 200;
	power = 100;
	
	event = mat_effUVinit;
	effect = "
	matrix matMtl;

	technique effUVspeed
	{
		pass one
		{
			TextureTransformFlags[0] = Count2;
			TextureTransform[0] = <matMtl>;
		}
	}
	technique fallback { pass one { } }
	";
}

---

Here's a screenshot using the .u and .v. You may not even be able to tell, but it's very noticeable during gameplay. The transparent vertical streaks are rain drops:

http://www.geocities.com/hainesrs/game/shot_0.jpg