I was having some issues doing a standard install of SQL Server 2005 SP2 (Standard). No matter what I did, the install complained about versioning issues. I knew you could blindly run a full install from command promt but I had never needed/wanted to. Out of desperation I decided to give the install a try from command the prompt and had great succcess.

setup.exe /qb INSTANCENAME=EGPS ADDLOCAL=SQL_Engine SAPWD=***** AGTACCOUNT=ComputerName\Services AGTPASSWORD=***** SQLACCOUNT=ComputerName\Services SQLPASSWORD=***** SQLAUTOSTART=1 SECURITYMODE=SQL

You'll notice I used an actual account name [Services in my case] instead of a System account for the logins. I honestly couldn't get this to work with a System account. I tried multiple variations, but came up short.

There are also many more options available and the above will just install the new SQL engine portion. You can also change the /qb to /qn and it will run silently.  Microsoft has an entire doc on setup options, but it was down/blank when I tried to use it. I ended up using a Google Cache Version of documentation.

This hands free install was definetly super handy and easy. I install and uninstall new instances all the time and plan on always using this in the future.