Thanks Lucid and everybody's else help on the plugins. I'm still learning about how code integrates with Construct's plugin system, but it isn't as challenging as I originally thought!
Here is a very early version of a screenshot plugin I am making. It only has one command right now, an action to take screenshot. The parameter for taking just the current screen doesn't work yet (it only gets the entire desktop), but I plan on adding that as well as adding option to name save file as well as auto increment the name of save file as you take more screenshots!http://www.box.net/shared/i28fdpvfj0
UPDATE: Added window-capturing and auto-incrementing file saves. Fixed bug in save location, an file naming, added expression to get screenshot count.