script,awk,sed question?

[Andrew Law]

Hello, I have two files:  
 file a                            file b
 with 'string 1' #n                with 'string 1' #1
      'string 5' #n                     'string 2' #2
                                        'string 3' #3
                                        'string 4' #4
                                        'string 5' #5
What I would like to do is to read file a and b. If there is
a match on the string in a to a string in b,  the #n will be 
substituted by the appropiate # number from file b.
Any suggestions on how to do with shell scripts, awk or sed.
Please send mail to andrewl at olivea.olivetti.com

Thank you very much.