If you are getting this error when trying to install Exchange Server 2007 SP1
The system cannot find the file specified
An unexpected error has occurred and debug information is being generated: The system cannot find the file specified"
you may want to check C:\ExchangeSetupLogs\ExchangeSetup.log for errors.
If the missing file is Ldifde.exe you should install ADDS.
For Windows Server 2008 R2 open Server Manager go to Roles, click Add Roles and install Active Directory Domain Services.
If you're installing Exchange 2007 Management Tools on Windows 7, simply copy the file ldifde.exe from your server to C:\windows\system32\ folder.