Dropping WP Into My Site – Is This Just A Theme?

I have my own design and basically, I want to treat WP like a CMS and drop in / customize this to fit my own selfish needs.

To make a long story short, I want to use the blogging functionality, the blogroll and other widgets and keep my own header and top-level navigation, as well as my footer. The home page has some image randomization and the navigation has states for “current page” “roll over” and “roll out” that I’d like to maintain as the site shifts from page to page.

None of this, from where I sit, is really all that complex from a “design and build a site” perspective, but I’d like to use WP to manage my content.

The issue here is that I’ve only used WP pretty generically until now and I’m needing to expand my usage a bit. I don’t know where to really begin, nor exactly how to search–an experienced WP person may tell me “you really are looking at just customized templates” but it doesn’t seem that way to me, so I’m looking for some help / a boot to the backside to get me in the right direction.

Thanks in advance!

P.S. I’m not necessarily trying to seek-out someone else to do this and I don’t want to violate any rules (sorry, I’m a newb on this forum), but I’m not against someone saying “I can do that for you for $X and it’ll be done in <timeframe>” or something so long as it’s going to get me to the desired result.