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HLSL particle fountain - help

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Hello, I have a problem with HLSL vertex shader. It's responsible for showing a particle system - fountain of water drops that are thrown from one point and then fall under the gravity. It works for displaying the particles, however I would like to render the result to the texture as well, so that I could know where the water drops hits the ground (like top view of the fountain). The problem is that I don't know how to translate particles to this texture space :-( Maybe you could help. Thanks in advance Omi.
   VS_OUTPUT Out; 
   float3 pos;   
   // The view matrix for right and up vectors.
   pos = particleSize * (In.Pos.x * view_matrix[0] + In.Pos.y * view_matrix[1]);   
   // S = UT+AT^2/2
   float T;  // Time for this particle
   float3 U; // The starting velocity vector  
   // Clamp time to a range defined by the length of the effect
   T = frac(In.Pos.z + 0.51 * Time_0_X);
   // random startig speeds
   U.x = cos(63 * In.Pos.z)*40*particleSpeed;
   U.y = 100*particleSpeed;
   U.z = sin(163 * In.Pos.z)*40*particleSpeed;
   // Work out the acceleration component
   float AT = (gravity*T*T)/2;
   // Only apply the acceleration component to the y position
   pos.y += U.y*T+AT;   
   pos.x += U.x*T;
   pos.z += U.z*T;
   // Converting to camera space
   Out.Pos = mul(view_proj_matrix, float4(pos, 1)); 
   return Out;
EDIT: Please remember to use 'source' tags. [Edited by - jollyjeffers on June 11, 2007 6:58:31 AM]

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Cannot you just use a standard VS to xform the data?
Then set up an ortho projection with a very limited znear/zfar range (the small plane).
Everything that gets rendered it's hitting the plane.

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