That's true, if it's massive, it'll force the page to have a horizontal scrollie, and no one ever wants that.
If you're feeling adventerous, here's an option for you.
Break the image up into two parts, the main part, and the black part off to the right (the part that you just have repeating). For this example, I'll call them main.png and repeat.png.
Then, you can remove the reference to <!--System:Logo--> in the layout.html file, replacing it with a pair of divs
<div class=logowrapper>
<div class=logo onclick="location.href='news.php'"></div>
</div>
Remember, that goes were the old Logo was. The "onclick" part is just for making the logo be a click-back to your main oage.
Then, in your CSS, you would define it like this:
.logowrapper {
position:absolute;
left:0;
width:100%;
top:10px;
height:200px;
background-image:url(http://dkpfiles.com/myth/files/repeat.png) repeat-x;
}
.logo {
position:absolute;
left:0;
top:0;
width:700px /* (or however wide your logo is) */
height:200px;
background-image:url(http://dkpfiles.com/myth/files/main.png) no-repeat;
cursor:pointer
}
Something like that. You'll likely need to tweak it a bit, but for the most part, that should take care of it. And the logowrapper will ensure that the top-bar repeats for however large of resolution a user has.