In 2.49 press F7 after selecting an object you want to apply a field to. Then choose the physics sub-context icon. The Fields TAB should appear.
But I think the answer is no if I am guessing your intent. You can not have object based particles carry their fields into the particle system. Fields affect systems, but the particles in a system can not have fields. Object and group based particles are only mesh based. If the object used in a particle system has a field applied to it, it will be ignored when that object is being deployed by the particle system.
In the example file, you can see a particle system deploying a cube with a vortex field. While the field is drawn by the particle system (why?) it has no effect on the other particle systems in the scene. However, there is an additional Empty in the scene that has a vortex field that does affect the other systems. Move it around to see the affect.