Err... Which post in there did you want us to look at exactly? There's quite a lot in there and we're not exactly which one we should be referring to? :'D
As to where to put Pluvy's code into yours, you're going to have to merge them with what's already existing rather than simply inserting the two divs. Since you're already using your outermost div as your scroll div, you can use this as the equivalent of the inner div of Pluvy's code. Currently you're using a percent value for the width, right? You're going to need to change this to a px or any other fixed value (e.g. 800px) for the cheat to work.
So your current first div is gonna look something like this: [spoili]
[div=background: #30382B url(http://i.imgur.com/02E4lfw.png) repeat center fixed;
border: 15px solid transparent;
padding: 15px;
-webkit-border-image: url(http://i.imgur.com/m2Et0lV.png) 20% round;
-o-border-image: url(http://i.imgur.com/m2Et0lV.png) 20% round;
border-image: url(http://i.imgur.com/m2Et0lV.png) 20% round;
width: <fixed value>;
height: 1372px;
overflow: scroll;
overflow-x: hidden;
margin: auto;
box-shadow: -2px -2px 30px 5px #170400;][/spoili]
Next step is to create a new div that wraps around everything you have so far. This will be the equivalent of the first div in Pluvy's code. As the fish mentioned, the width of this needs to match the width that you've previously set, so do that. Add overflow:hidden to it as well, and that's pretty much it. Your scrollbar should now be hidden.
Code thus far (for the two divs): [spoili]
[div=width: <fixed value>; overflow:hidden;
][div=background: #30382B url(http://i.imgur.com/02E4lfw.png) repeat center fixed;
border: 15px solid transparent;
padding: 15px;
-webkit-border-image: url(http://i.imgur.com/m2Et0lV.png) 20% round;
-o-border-image: url(http://i.imgur.com/m2Et0lV.png) 20% round;
border-image: url(http://i.imgur.com/m2Et0lV.png) 20% round;
width: <fixed value>;
height: 1372px;
overflow: scroll;
overflow-x: hidden;
margin: auto;
box-shadow: -2px -2px 30px 5px #170400;][/spoili]
Unfortunately, it does more than cut away the scrollbar, it also cuts away your borders. That's easy to fix tho, just move your borders to the first div and that should fix things. I suggest moving your box-shadow here as well as that gets cut away too. Move the margin:auto here as well to centre it.
Final code should look something like this: [spoili]
[div=width: <fixed value>; overflow:hidden; margin: auto; border-image: url(http://i.imgur.com/m2Et0lV.png) 20% round; border: 15px solid transparent; box-sizing:border-box; box-shadow: -2px -2px 30px 5px #170400;
-webkit-border-image: url(http://i.imgur.com/m2Et0lV.png) 20% round;
-o-border-image: url(http://i.imgur.com/m2Et0lV.png) 20% round;
][div=background: #30382B url(http://i.imgur.com/02E4lfw.png) repeat center fixed;
padding: 15px;
width: <fixed value>;
height: 1372px;
overflow: scroll;
overflow-x: hidden;][/spoili]
How do I separate the 'fields' or 'borders' so that they aren't within one another but have them as separate boxes within the same post?
Add their respective closing tags before the openings of the next one.
For example:
[bg=purple][fieldbox="Box One, black, solid"]Lorem ipsum dolor sit amet, consectetur adipiscing elit. Duis blandit arcu eget dolor lobortis condimentum. Quisque volutpat ante in felis vulputate, vel pulvinar risus aliquet. Quisque in turpis porta quam scelerisque ullamcorper eu ut arcu. Donec rutrum tincidunt neque. Quisque maximus nisl non sapien facilisis mattis. Etiam ac felis pellentesque, semper risus faucibus, dignissim tellus. Mauris vitae lorem ut enim ornare volutpat. Aenean auctor nulla mauris. Interdum et malesuada fames ac ante ipsum primis in faucibus. Morbi mi enim, vulputate vel ipsum ut, varius porta nisl. Phasellus vel ante dui. Nunc condimentum tellus augue, non ultrices lorem viverra id. Etiam placerat ante scelerisque purus ornare suscipit. Ut dapibus enim nec fringilla sagittis.[/fieldbox][/bg]
[bg=purple][fieldbox="Box Two, black, solid"]Lorem ipsum dolor sit amet, consectetur adipiscing elit. Duis blandit arcu eget dolor lobortis condimentum. Quisque volutpat ante in felis vulputate, vel pulvinar risus aliquet. Quisque in turpis porta quam scelerisque ullamcorper eu ut arcu. Donec rutrum tincidunt neque. Quisque maximus nisl non sapien facilisis mattis. Etiam ac felis pellentesque, semper risus faucibus, dignissim tellus. Mauris vitae lorem ut enim ornare volutpat. Aenean auctor nulla mauris. Interdum et malesuada fames ac ante ipsum primis in faucibus. Morbi mi enim, vulputate vel ipsum ut, varius porta nisl. Phasellus vel ante dui. Nunc condimentum tellus augue, non ultrices lorem viverra id. Etiam placerat ante scelerisque purus ornare suscipit. Ut dapibus enim nec fringilla sagittis.[/fieldbox][/bg]
Code: [spoili]
[solid=purple][bg=purple][fieldbox="Title one, black, solid"]Content goes here.
[/fieldbox][/bg][/solid]
[solid=purple][bg=purple][fieldbox="Title two, black, solid"]Content goes here.[/fieldbox][/bg][/solid]
[/solid][/spoili]