get the direction vector from vertex 1 to vertex 2

spawn the particals at one vertex1,
effect (function, var number, VECTOR* pos, VECTOR* speed);
in the VECTOR* speed parameter insert the direction vector you got from above.

set the particals lifespan = 0 ( or 1) mess with this depends on the distance from vert1 and vert 2

and set the particals streak flag on.


try that