localhost login: setup
Enter hostname[]: acs-server-1
Enter IP address[]:
Enter IP default netmask[]:
Enter IP default gateway[]:
Enter default DNS domain[]: mycompany.com
Enter Primary nameserver[]:
Add/Edit another nameserver? Y/N : n
Enter username [admin]: admin
Enter password:
Enter password again:
Pinging the gateway…
Pinging the primary nameserver…
Do not use `Ctrl-C’ from this point on…
Appliance is configured
Installing applications…
Installing acs…
Generating configuration…
After the ACS server is installed, the system reboots automatically.
Verify that the application has been installed properly by entering show application.
Check the release and ACS version installed  by entering show application version acs
Check the status of ACS processes, at the system prompt by entering show application status acs


Password Reset

– Power up the appliance.
– Insert the ACS 5.3 Recovery DVD.

The console displays:

      Welcome to Cisco Secure ACS 5.3 Recovery                                 
To boot from hard disk press <Enter>.                                          
Available boot options:                                                        
  [1] Cisco Secure ACS 5.3 Installation (Keyboard/Monitor)                     
  [2] Cisco Secure ACS 5.3 Installation (Serial Console)                       
  [3] Reset Administrator Password (Keyboard/Monitor)                          
  [4] Reset Administrator Password (Serial Console)                            
  <Enter> Boot from hard disk

In my case I used option 4 since I was connected via console.

The console displays:

  ———————— Admin Password Recovery ————————

  This utility will reset the password for the specified admin username.
  At most the first five admin usernames will be listed. Enter Ctrl-C
  to abort without saving changes and reboot.


  Admin Usernames :

     [1] admin

  Enter number of admin for password recovery: 1
  Verify password:

  Save changes and reboot? [y/n]: y



Source: http://www.cisco.com/en/US/docs/net_mgmt/cisco_secure_access_control_system/5.3/installation/guide/csacs.pdf