Major headaches with header element positioning!

[AudioPro]

Unlike quite a few shop users, I'm a manufacturer, that also sells service parts, so I'm not really a retailer per se. As such my site requirements are quite a bit different from what most people will find functional in existing themes. I'll also be attacking this thing in pieces so hopefully people will find my journey quite useful from a somewhat different perspective.

Now, to the problem. I'm working on building a theme that's consistent with the look of my existing website. I'm using the newest 1.3 stable version and I'm completely lost as to what to modify and how. Looking at a 2000 line css document is a bit intimidating to say the least and I can't quite seem to figure out which tags to modify and where to get the look that I want.

These are the main issues I'm having;

1. I'm not sure what tags to modify to get the header_user and nav elements placed where I need them;
(this one is the biggest issue right now. I think I'm finding the css tags but either nothing happens OR the results are significantly different than expected)

2. how would i insert or modify header_links to emulate the navigation bar somewhat as illustrated.

While the html and css aren't the cleanest thing ever, it all validates and I've tried to hold to the prestashop structure as best as I could. You can see an example page here...

http://valvetech.byethost14.com/shop/

of what I'm shooting for. It was kind of a quick an dirty mock up so it probably wont look quite right in IE.

There are other issue's I'm trying to sort out but I'd like to get the biggest issues done first and go one step at a time. I know I'm asking a lot in one post so any help with any of what I've outlined above would be greatly appreciated.

Thanks in advance
-Carl