I need to create a road like space in my particles. How can this be done using an .jpg as a distribution map. Can I use a vertex map for this or can I use an image like a .jpg to distribute the as a vertex map?
pg
Texture can only influence particles as Force Fields in 2.5.
In 2.49, you can set texture influence through Part button in Map Input of Material when the mesh is a particle emitter.
http://wiki.blender.org/index.php/Doc:Manual/Physics/Particles/Controlling_Emission,_Interaction_and_Time#Textures_controlling_particle_attributes
Thanks zeauro. So it can be done in 2.49 but I am using 2.5. Is there another way? Not sure what you mean by “Texture can only influence particles as force fields in 2.5” Does this mean I can use an.jpg image in the Force Field space. Please explain. 
If there is another way to do this I’d really like to know. I want to control where my particles appear.
pg
When you want to influence particle trajectories, you can use a Force Field to create wind, for example.
http://wiki.blender.org/index.php/Doc:Manual/Physics/Force_Fields#Texture_field
It will be difficult to obtain a correct result with that.
In 2.5, it is simpler to use a mesh.
Add collision for the mesh and activate Kill Particles option.
It will kill Newtonian Particles.
But maybe you don’t need to animate Particles and Dupliverts with a noisy grid can do the job.