[link|http://members.fortunecity.com/cdmadness/turniton.html|Turn It On] is a working link. I haven't tried it myself, but I've been looking for something like that for a while. (I use the Marqee screen saver to leave notes while I'm away from my desk, but I'd like a trivial way to change the text and activate it without clicking around so much.)
Actually, it seems impossible to find the executable anywhere, so it's still a dead link. :-(
MS also has [link|http://www.microsoft.com/windowsxp/using/setup/learnmore/tips/liu1.mspx|this] tip for activating a screen saver of your choice with 2 clicks. Unfortunately, there's no simple way to access the properties to change the parameters with this method.
I guess I'll have to get off my butt and figure out how to poke at the registry with Python.
[edit:] [link|http://www.softpedia.com/get/Authoring-tools/Screensaver-Tools/Marquee-Launcher.shtml|Marquee Launcher] does what I want. Why it requires 775 kB to do it is beyond me... It works pretty well.
Cheers,
Scott.