Page 17
                                                             Exhibit 10(iii)A(c)

                                  May 24, 1996



J. Robert Hipps
5021 Northside Drive, N.W.
Atlanta, Georgia   30327-4421


         Re:      Amendment of Stock Option Agreements


Dear Bob:

     In connection  with your  termination of  employment,  and as confirmed and
evidenced  by  this  letter  agreement,  the  terms  of  certain  stock  options
previously granted to you were amended by action taken by the Executive Resource
and Nominating  Committee of NSI's Board of Directors (the "Committee") on March
20, 1996, and ratified by the Board of Directors on that same date.

     The following  installments of employee stock options, which had previously
been granted to you and which would otherwise have vested and become exercisable
in  September  1996,  have  been   accelerated  so  that  they  are  immediately
exercisable on this date:

                                                                Number of
                       Option Grant Date                 Shares In Installment

                      September 16, 1992                         2,529
                      September 16, 1992                           471
                      September 15, 1993                         2,671
                      September 15, 1993                         1,079
                      September 21, 1994                         5,000
                      September 20, 1995                         5,000
                                                                16,750

     In addition,  the  Committee  amended the  expiration  provisions  of those
options for 16,750  shares and options for 32,364  shares which were  previously
granted to you and were already exercisable  according to their original vesting
schedules.  Pursuant to the  amendment,  said options for 49,114  shares  remain
exercisable through May 31, 1997, notwithstanding your resignation effective May
31, 1996.



                                                                         Page 18
                                                             Exhibit 10(iii)A(c)
Page 2
J. Robert Hipps
May 24, 1996



     Your Incentive Stock Option  Agreement dated September 19, 1990,  Incentive
Stock Option Agreement dated December 18, 1991, Incentive Stock Option Agreement
dated September 16, 1992,  Nonqualified  Stock Option  Agreement dated September
16,  1992,   Incentive   Stock  Option   Agreement  dated  September  15,  1993,
Nonqualified Stock Option Agreement dated September 15, 1993, Nonqualified Stock
Option  Agreement  dated  September  21,  1994,  and  Nonqualified  Stock Option
Agreement  dated  September  20, 1995 (the "Stock Option  Agreements")  are each
hereby amended in accordance with this letter.

     Please  acknowledge  your acceptance of this letter by signing in the space
provided below and returning the executed  letter to me. A duplicate is enclosed
for you to retain with your copies of the Stock Option Agreements.

                                           Very truly yours,




                                           /s/ James S. Balloun
                                           James S. Balloun
                                           Chairman and Chief Executive Officer

JSB:sdh
Enclosures

Accepted and agreed to as of the
24th day of May, 1996:



/s/ J. Robert Hipps
J. Robert Hipps