Try the installation again using a valid copy of the installation package 'sqlncli.msi'
Problem:
If SqlServer 2005 Setup fails and roll back with the following error message:
"An installation package for the product Microsoft SQL Native Client cannot be found. Try the installation again using a valid copy of the installation package 'sqlncli.msi'."
Reason:
It’s probably due to the fact that you have installed .NET Framework 3.5 BEFORE you have installed SqlServer 2005 ;)
Solution:
To work around this problem, uninstall SQL Native Client by using Add or Remove Programs. On a cluster, uninstall SQL Native Client from all nodes. Then, run SQL Server Setup again.