MacOSX has some issues I ran into, because I don't expect the way it works on a Mac. Well I don't think this has benefits:
Keyboard layouts are organized in .xml files on a mac. The system looks in /Library/keyboard Layout or in ~/Library/Keyboard Layout. You can download a nice german pc keyboard layout for a standard windows keyboard from http://www.nullpointer.de/stuff/keylayout/index.de. Copy it into the folder, open system preferences, language & text, check pc-keyboard from inputsources and also the keyboard and char overview. Then you can easily change your keyboard layout by using the icon in the apple bar.
MacOSX has no native support for using additional mouse buttons. You have to install a mouse driver for this. E.g. for logitech mice look at http://www.apple.com/downloads/macosx/drivers/logitechcontrolcenter.html. The mouse acceleration looks like a bug, one can fix that with iMouseFix