Yay! Thank you, Null54! The site your link points to works!
On Saturday, since I found no Download button on the Paint.net site, I assumed -- and we know about those who assume, right? -- that the correct site must be GETPAINT.NET. (Today's getpaint.net site has dropped the urgency to download WinZip, and instead wants you to download a Yahoo-sponsored Search program to replace my Google search bar.) Using the site suggested by Null54 yields paint.net.4.2.11.install.zip, which I unzipped with my fave, 7-zip! Paint.net installs beautifully and is so easy from there -- I'm already working on my first picture in paint.net.