I got blender 2.6 recently. I was trying to put hair on one of my character, however, everytime i go to particles mode the program stops answering and after a few seconds it shuts down. I have try several times, I restarted the computer and nothing

Try running blender from the command line to get interesting messages.

If I had to guess, I would say you are running out of memory. If so, you will see messages about 'calloc returns nil' and some big numbers.