how do I make a specific desktop background the default in xp

From: ronram_25 (ronram_25_at_discussions.microsoft.com)
Date: 10/17/04 

Date: Sat, 16 Oct 2004 18:27:01 -0700

I would like to make a specific desktop theme the default in xp, so when
users login they cannot change the theme. I would like to do this from the
registry.