This is actually a pretty simple layout, it includes a tiled background and a sidebar. A good place to start (especially if you have a basic understanding of HTML/CSS) is by looking at the S1 Generator Walkthrough
and the Livejournal FAQs
Otherwise, we have several Livejournal layouts
for you to look through - see if there's something you like. If you decide you might want to alter the layout (take the code and change the images to make it look different), it's always a good idea to ask the author of the layout first, but if you want a few to get you started, I have a few here
that I don't mind if you change.