Thanks, Idris, those screens are coming in handy, and will come in even handier in the future.
Adam (whose screen name escapes me) brought in a roll of screen that I thought was the right size for both windows; I had a brain fart, it was enough for 1, with some scrap left over.
I removed the plastic from one of the wood frames that had sealed up the windows over the winter, and put screen on it instead.
So, now, for the right window, we can take out the glass and friction fit the wood frame in the window, as long as we replace the glass when people leave, due to water.
I'm going to look at mounting the screen outside so it can just stay on all the time.
Another roll of screen would be handy, if anyone gets motivated; if we don't get some, I'm going to take a stab at making a frame for Idris's windows so they can be used, without destroying them.