Change in design problem

This is a huge newbie question (or at least a huge one for me), but I finally created my site a few months ago (from my own design but with help from someone I cant get help from again), and now Im feeling its just not me.
Everything is good except for a couple things with the style, and I dont know how to go about changing the style without having to re do everything!

so my current site is: http://www.snapcracklerock.com

and I want it to look like this (another design by me): http://i20.tinypic.com/2q33pxj.jpg

So what changes will be curved edges, dark grey background & white blog inside, 2 in 1 column look, and a shadow around the curve border.

Is this possible without changing everything and if so how do I figure out how to do this?