You already asked this in a different thread.

My response was :

You shouldn't have any problems if you change the
password for the ASPNET user account via user manager.

re:
!> W2k3 servers running IIS 6.0 and .NET 1.1.
!> Is there a way to determine the current password, in case we want to roll it back?

I don't recall a single instance of a setting where you'd have to supply
both the "NT Authority\Network Service" account *and* its password.

Just supplying the *name* of the account is enough.
The user manager supplies the password.

If you change the password, the user manager will simply use that new password.

Notice : "NT Authority\Network Service" is the default "ASPNET" account for W2K3
( that should have been "ASP.NET" account, not "ASPNET" account.

"ASPNET" is the default ASP.NET account for Windows 2000 and Windows XP,
which run IIS 5.0 and 5.1, respectively.

You are running W2K3, which runs IIS 6.0 and uses the
"NT Authority\Network Service" account as the default "ASP.NET" account.

Juan T. Llibre, asp.net MVP
asp.net faq : http://asp.net.do/faq/
foros de asp.net, en español : http://asp.net.do/foros/
======================================