There's an attribute for particle velocity or something like that. Try playing with that.
And maybe this could help you:
Code:
function p_fountain(PARTICLE* p)
{
   VECTOR vTemp;
   vec_randomize(vTemp,2);
   vec_add(p.vel_x,vTemp);
   vec_set(p.blue,vector(random(255),random(255),255));
   set(p, MOVE | BRIGHT | TRANSLUCENT);
   p.alpha = 100;
   p.size = 2;
   p.gravity = 0.2;
   p.skill_a = 3; // fade factor
   p.event = p_alphafade;
}



Ubi bene, ibi Patria.