Ooh! Thank you!!
Does it work on an actual livejournal page, by typing into the box used for journal overrides? Could I place two frames on either side of one empty journal?
I'm quite positive that the "Overrides" box isn't where you'd put this in. If you read the description above the override box, the only things you can use in this box are "<.title>, <.base>, <.style>, <.link>, and <.meta>". To do what you want to do with the community, you would have to be able to create a Style, and you can't do that without a paid account.
The best thing you could do is create a page with the frames offsite, and link to it. (That is, unless you want to pay for an account so you can create a style).