Windows 7: Help| changing login screen look

hello people of 7forums
i saw this login mod on deviantart link
i wanted to try it but the thing is i can't replace the original
i have took ownership of the authui.dll file.
when i renamed it to authui_original.dll and i paste the new file it doesn't paste there.
and when i try to renamed the original file back, it doesn't either.
i am just curious why i does that.



windows 7 64bit 7600
i have not done any mods to my login yet. neither the background change

maybe this will help:

Log On Screen - Change

yeah i am aware of that. i have done that before
but the mod is completely change the whole look of the log in screen as you can see form the link