I solved the problem. It´s no jQuery problem. What you just have to do is to change the float-part from the headlines at your style.css in the snowblind folder:
line 40:
h1, h2, h3, h4, h5, h6 {
width: 100%;
float: none; /*default value: float: left;*/
clear: both;
line-height: 1pt;
}
I figure it out with the great firefox add-on "firebug" where you can disable css parts. So also thx to the add-on author(s).
But there was still another problem. If you want to show just one image at your slideshow-widget the pictures aren´t centered in the sidebar.
So if you have a upride- or highside-picture (i don´t know how you call it:-)) the image isn´t centered.
You can center the images in the widget by changing your widgets.php (\plugins\nextgen-gallery\widgets) on line 308 from this:
echo "\n" . '<div class="ngg-widget entry-content">'. "\n";
to this:
echo "\n" . '<div class="ngg-widget entry-content" style="text-align: center;">'. "\n";
I hope this can help somebody else, too.