Bartik theme main menu I am dabbling fresh with Drupal 7 and so far having little success with getting the Menu to behave the way I want it to. My CSS and PHP basics are strong, but understanding Drupal's system is in itself a huge challenge and hence my doubts.

For those acquainted with the Bartik theme, the main menu defaults itself in the header. 

I am trying to create a floating/persistent menu that encapsulates the entire width of the website. But I am not sure where I need to go in and make the required changes.

One option I have is to remove the main menu from the Bartik header and then introduce the main menu block in the 'featured' region. Here the menu is rendering itself horizontally instead of vertically the way i want it to be.

Essentially the question is, How do I alter the main menu in the Bartik theme? Where do I need to get in and make changes.OH, and I have sub-themed it, just to let you know.
Take a look at the module Nice Menus or Superfish menus.  Both offer a lot of flexiblity and control for managing menus.  In both cases you will configure the module to provide some menu blocks and configure the blocks to attach them to your main menu.  You will then put the Nice Menu (or Superfish) block where you want it and hide the main menu block.  (I like superfish)