Can you give an url of your page using that skin? That could help us find the problem bit of code. You don't have to change the setting in the backoffice, just give an url for displaying it, like this:

http://wifi-wue.de/?skin=yourskinname

Also note that those instructions are good for WordPress 1.2. They're at 1.5 now, so the skins may not be compatible any more.

Also check that all your div's are in fact closed

Sure I can provide you with some links. You can try these two:

http://wifi-wue.de/weblog/b2evolution/blogs/?skin=Connections

http://wifi-wue.de/weblog/b2evolution/blogs/?skin=FastTrack

Maybe it is because these are Wordpress 1.5 Styles...

I'm assuming that this section of text is meant to be a footer:

powered by b2evolution
Dieses Skin nutzt eine CSS-Datei, die ursprünglich für WordPress entwickelt wurde (siehe Design Credits in style.css).
Um maximale Kompatibilität mit WP CSS Dateien zu gewährleisten, sind die meisten Features, die nicht in WP vorhanden sind, in diesem generischen wpc_* Skin versteckt.

If so then, put this before it:

<div clear="all">

and this after it:

</div>

And see if that helps.

Cool, Thanks!

Meanwhile I tried to build up my own skin:
http://wifi-wue.de/weblog/b2evolution/blogs/?skin=custom

Looks great.