How do you write your own books in the construction set? I've tried searching around for a mod that lets you do it, but no luck (any links?), so I'm going to try it myself. But my skills in modding anything other than quests are useless, so I need help. Thanks.

You can do this in the latest version of OBSE, I believe. I'm not exactly sure what the function is, but I've seen mods that do it. For example:
http://www.tesnexus.com/downloads/file.php?id=15294 manages to do it quite well.
It's easier to do in the Construction Set though. Just go to Items>Books, select/create/duplicate a book and double click it. All of the text in it can be found under the 'Book Text' window.

Hope that helped!

EDIT: You'll need OBSE V16 to do this; and so will the recipient.

Thanks. There's a new OBSE? How do I install it? Do I just download it, and then run it, and it's done? Or is it different?

I think there may even be an OBSE V17 now. You can find out the latest builds on http://obse.silverlock.org/.
For any installation instruction, follow http://cs.elderscrolls.com/constwiki/index.php/Obse.
The newest version installs just like the old ones did; you may want to delete the folder (in your Oblivion folder, most likely to be called 00[Numbers]) just to be sure!

Good luck!

If you want to make a book in the CS to place in game, I know of no better tool than Critterman's http://tesnexus.com/downloads/file.php?id=29124.