particle collision (2.5)

Hi! In my animation I have streamers(hair particles) attached to bicycle handlebars and I need them to hit a shelf (don’t ask) but I have one problem: the streamers go through the shelf.
Is there a way to make the particles collide with the shelf instead of going through it? Thanks!
I’m using blender 2.5.

Go inside the physics panel and enable collision on the shelf. Check this out: