Silent SQL Server 2005 Installation is possible in two steps.
1) Creating an .ini file
The SQL Server CD contains a template file called template.ini . Based on that create another required .ini file which includes a single [Options] section containing multiple parameters, each relating to a different feature or configuration setting.
2) Run Setup on command prompt
On command prompt type following script
setup.exe /settings <path TO .ini FILE>
If location of sqlinstall.ini file is at C:\SQLSetup folder. The command to initiate silent installation is:
setup.exe /settings C:SQLSetup sqlinstall.ini
Specify the /qn switch to perform a silent installation (with no dialog boxes) or the /qb switch to specify that only progress dialog boxes should be displayed.
Reference : Pinal Dave (http://blog.SQLAuthority.com)