organization chart (organigramm)

Welcome to the forums, alphaville. Unfortunately Keynote doesn't have the kind of charting-specific features that PowerPoint does, such as "smart" connectors -- it only has basic drawing tools (shapes, lines, etc.). It can import charts from a variety of sources, including PowerPoint, although once in Keynote the chart will not be editable.

PowerMac G5 Mac OS X (10.4.4)

Give OmniGraffle a try. It is much better than PowerPoint content, and if (once it comes out for Keynote 3) you add in the LinkBack plugin to Keynote you can/will be able to edit the files after you embed them into Keynote.

Mac OS X (10.4.6)

Alphaville,

I second larkost's suggestion to use OmniGraffle. Since you've got a PowerBook, OmniGraffle should already be in your Application folder (in German: Programme). It's probably not the latest version but you can get an impression of what it does.