Malcolm,
I use a VB program called Niteview.
http://www.astro.ufl.edu/~oliver/niteview/
Runs in the background and has user selectable options.
While it doesn't totally redden all types of screen very well
(IIS site and general browsing for example), it does a good job on
my Imaging capture and preview screens and also on Cartes Du Ciel
and Starry Night (even though these both have built in Night vision)
Steve