Then change the CSS so that the navigation is displayed as a block, then you can define the colours you want.
Use the top image that you have don in photoshop and get rid of the current one.
Play around with the index file and take out any of the code that you dont need and take away some of those borders.
All CMS's can easily be modded by simply going thru the index file and the CSS file then simply creating the images.
Although you say you have just got your head round this, have you heard of Joomla? That would be perfect for that site that you are looking to create. The navigation and layout is very similar to a website we have created, www.prestonconservatives.com and this was created with Joomla.

Craig