the “left” side – the menu, doesn’t run completely to the bottom & top of your page, it is boxed off so it would look .. boxed off. If you want you can try though. The left side background can be entered by adding this to your style.css file in the .sidebar class.
to change the right background you can addbackground: #99bbaa; to .content – also in your style.css
As for your submenu’s you’d have to edit quite some code to make this happen. You can, however make a menu item for every “sub” product and just name the parent Products and the others – Products A with a dash in front of it, so you get the feeling it is a subheading.