open files options

I recently rebuilt my Pc and now find that an option for viewing files
with a program titled "Windows help executable" or similar name. I'm not
sure of the title but it was listed under "open with". Can anyone
advise me of what that program was and how to get it back. When using
outlook express, the files showed all of the hidden symbols. When using
this program the file displays properly. Any help or advise will be
appreciated. I'm using XP PRO SP2.