OK, I set this up and it works:
RewriteRule ^(.*)$ http://www.myblog.com/blog/$1 [R=301L]]
However, I still have one very important problem to work out. Now that the old blog links are pointing to the new blog links, I also want to do something unorthodox. I have another directory that I want to make the main section of my entire website, and it currently resides at http://www.myblog.com/gallery
I want to make people coming to http://www.myblog.com to instead be forced to go to http://www.myblog.com/gallery.
So do you follow me on all this? I want to do 2 things, and the first thing is already working:
1) point myblog.com/%year%/%monthnum%/%day%/%postname%/ to myblog.com/blog/%year%/%monthnum%/%day%/%postname%/
2) If anybody goes directly to http://www.myblog.com (the old homepage of the entire site), they will instead go to http://www.myblog.com/gallery/
For the second idea above, I tried this code:
Redirect 301 /index.php http://www.myblog.com/gallery/
If I use that ALONE (without the RewriteRule code I mentioned at the very beginning), it works fine. However when I use the code for #1 and #2, only the #1 code works and the #2 code doesn't work at all...