Devious little thing, but I see that the trick with that image is that it's 363 pixels wide (the width of the box), but only 1 pixel high! So, if you tried copying the URL to your browser's address bar, you'd barely see anything except short smudges of what makes up the left and right "border" of the text box against a practically all-white window - but it's there.
Anyway, you did say you managed to save a copy of it, so the above should be known to you already. Now, all you have to do is just upload it to your photobucket together with the other images, then copy the "Direct Link" URL provided. If it provides you with a URL with a ? sign somewhere at the end like your top and bottom image, just delete everything from that sign onwards (or don't, if it works well enough for you - some users just experience posting problems when they keep the ? sign and everything after that).
Here's how the image looks against a black background, by the way:
If you quote this reply, you'll see the Direct Link URL of it as it can be found in my photobucket, and once you upload it to your own photobucket, this should be the form you'd be putting in the background= part of the HTML Table tag, like the way it works below:
Essentially, it's a 1-pixel image that gets repeatedly tiled upon itself for every pixel of your text area's eventual height (as it expands as you type in more text). So, in short, just upload a copy of this 1-pixel high image to your photobucket, get the Direct Link URL (delete ? sign onwards), and paste it over the old groups.msn.com address printed in the original coding.
Here's how it looks like as a whole with the background image linked from my photobucket and the top and bottom from yours. It's no longer any different than your original box:
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"There's a method to my madness; if only I could find it..."
Problem Solved. Merry Christmas.