5. It's definitely a gradient, so your best bet is to use a PNG with a transparent background.
If you haven't already, install Firefox and add an add-on called Firebug. It will show you how a website is structured. Also, in the General Settings>Add Template Name in HTML Comments set that to 'yes' while working on your site. It will add comment lines in the View Source so you can see where templates start and stop.
I also came to this with rudimentary knowledge of HTML and CSS, and it's different to have new layers of building blocks to work with. It helps to study up on templates and phrases in the manual:
http://www.vbulletin.com/docs/html/