Are you just wanting the box to popup with the login fields etc. displayed rather than an entire page dedicated just to logging in?
Our web-wizard at work manages to accomplish some pretty impressive things with just the showing and hiding of various <div> tags within a page itself. He's quite fond of Fancybox
, and try the "Add Request For Beta Invitation" link for an example of the showing/hiding <div>s.
I've been picking at HTML5 and CSS3 lately in an extremely rudimentary fashion (mostly text-related stuff for e-Book typography), but I've found the tutorials on http://w3schools.com/
to be incredibly helpful. It's definitely geared towards beginners, so you may find it just rehashes stuff you already know.
One thing we've done at work for major websites is just use a WordPress installation as the base of the whole thing. With a little tweaking and a willingness to maybe spend some money on a professionally-created theme, it's really amazing what you can come up with. Our company homepage runs the inFocus theme (demo here
), and I really like its handling of drop-down menus. You might consider something similar because of the blog-like nature of content on the non-forum part of the site.