OH .. it didn't work? Did you try restarting via your installation disk? Choose from menu instead of using the installer ... to get to desktop.

Another alternative. Set up an alternate account, quite easy: Setting up a Test Account in OSX (click on link) & delete it from there.

I can't find any reference to me posting about my experience before. Pity I cannot remember what I did.

And no you won't be able to delete that file whilst LW is open. The issue is to make that file inactive from the system. It is somehow stopping the present operating system from deleting it, so if the computer is running under a different user account with different permissions or a different startup owner, etc. it might make it lose its power.