(Credits go to Caligula for the work-in-progress fix)
The problem with the keyboard (missing keys, eg AltGr)
has a Work-in-progress fix..
If you have CVS, you can add support by following this thread..

german layout (bottom of the page for newest D/L)

Or wait for the next exciting episode of dosbox 0.61.

For those of you wondering what the keyboard looks like:
http://www.mag-murphy.net/temp/germankeys.png