Hi Invisible,
I don't know of a MS tool to change the SID. there probably is one in the NT
resource Kit, but seeing they expect money for it (and it isn't available
anymore anyway) I always going looking for public domain tools that acheive the
same aim.
There is a really nice SID management/change tool made by Systems Internals
http://www.sysinternals.com/ntw2k/source/newsid.shtml
It is GUI based and looks very straightforward. I don't know how well it works,
I haven't yet been presented with an opportunity to 'use it in anger'. Have a
look at it when you get a chance.
Calvin.