Transparent window-border?
 

Is it possible to get it on SLED 10 with KDE? Any ideas or how-to's around?

I hope it will come with its DVD itself.

goto yast -> software management and search for kde and install it.

I got KDE, but not transparent window-borders - that's what I need, not KDE :)

I'm using the crystal window deco from www.kde-look.org. It makes pseudo-transparency using a clip that it makes from the desktop. Is that what you're looking for?

They seem to be available if you have some kind of 3D effects provider? Or can they be installed without it?

This is the one I mentioned:
http://www.kde-look.org/content/show.php?content=13969

I have seen some that require hardware accelleration, composite extensions, etc, but this one doesn't. That's one of it's strengths that makes it popular.

If you want the compviz effects you have in kde to work in kde as well, then google with the terms: cool solutions suse compiz xgl kde

If it is the kde window transparency effects you want then add
to xorg.conf and enable effects in kde. You can access the configuration by right clicking on a kde window border or through KMenu -> Personal Settings -> Desktop -> Window Behavior -> Translucency.

However, I've found that this slows down performance to an unacceptable level.

I installed Beryl/Compiz and my computer is already being slower. I will remove it asap. The crystal window decoration did not slow down my computer, so I will stick to that one.

In fact: My whole system is slower now, even after I removed Beryl/Compiz :( What have I done now...!?