I just noticed that the area where I can create a custom block mentions a "useful tag": {X_SITEURL}. Are there more tags like this, and if so, where do I find the list. (I've spent quite a bit of time looking through the site with no luck.)

I'm also wondering if there's a tutorial for the custom block that would show me how to use PHP with it. I know HTML, and am pretty comfortable with CSS, but PHP is totally new to me. Among the blocks I'd like to be able to create are ones to: display a single forum, display the contents of a single weblinks category, and display the title and teaser of all the articles in a single category.