Simple Mouse Dragging Thing

I got an e-mail a few days ago from someone (who saw my site, who got my e-mail from here, who knows) asking me for a tutorial on using the mouse to select an area on the form. So, I whipped up a little thing. Normally, I wouldn't post this kind of thing here (as I don't totally see exactly how useful it is), but this guy was extremely happy I wrote this little thing. That makes me think it could be valueable to others here. So, attached is a few lines of code (not much, really) demonstrating simple mouse techniques. It's fairly well commented, so I hope it's of use to a few people.