Sorry for being such a xoops newbie, but I followed all the steps above and I cannot get the checkbox to show up at all. I see it in the login block code, but it is never displayed on my website. It seems like it must be something to do with cache but I cannot get it to overwrite the old login block anywhere. Any help is appreciated.
Perhaps, you don't know the appropriate method for customizing template.
The easiest and best way
Install tplsadmin.
Go to system.
Edit system_block_login.html
you'll do it.