so to my knowledge particle hair collisions aren’t really working in blender 2.5 (as in when you turn on collisions for objects in the physics panel, hair strands still seem to pass freely through them). if i’m mistaken or missing a step, feel free to chime in, though!
anyway, i’ve found what seems to be a useful work around that can help in at least some cases. instead of setting collision physics for an object, give it a force field with settings like the following:
type: force
shape: surface
strength: something high like 100-200
falloff power: i use between 2 and 4
use maximum: set this to a reasonable distance so that hair appears like it could be contacting the objects surface, but still enough that it essentially creates a “shell” of outward force all around the colliding object.
one other note, if the colliding object is the emitter itself, you seem to have to make a duplicate version of the emitter object (that you can just set to invisible when rendering) as the particle hair seems to ignore forces generated by its own emitter.
