You use neither tables nor iframes. You use CSS, put your content in DIVs on the HTML page and position them via CSS (either internally or in an file you call).
I think you should find a book that teaches XHTML and CSS together, or HTML if you can’t find an X one (the only difference is that X is more rigid, and you need to add certain closing elements to stand-alone tags, and a few other small things, it’s really not a different language at all). HTML for the content, CSS for the design and positioning.
XML I would rank pretty low on the list, and it’s not really a language you learn, more as you simply understand how its structure and hierarchy works and voila there it is. Javascript is a bit more intense and you’ll likely want to have a handy guide to look things up for, but it’s all well documented and if you learn it on an as-need basis as I often do, it’s easy to eat in small pieces.
Ah, here’s the site I was talking about before: CSS templates. I often start my designs using these, as they’re valid and perfect, why reinvent the wheel! Download one of those and take a peek. It’s very easy to understand, and a good way to start playing with HTML without having to worry about the rest of the document, etc.