After some struggling with the default installation I finally got it working. The main problem were missing UAMs, the default debian package just supplies them for guest, cleartext and kerberos. I think it's because of some legal issues within Debian ... .
So I downloaded the netatalk-sources for version 2.02 and tried to compile it for myself. Unfortunately this didn't work out, as it wouldn't produce the neccessary UAMs. I searched the web and found this usenet post
(it's in german). The main point is to have some libs installed:libdb4.2-dev,
are needed, I used ./configure --prefix=/usr --sysconfdir=/etc --enable-debian --with-shadow --with-pam
to set everything up. Then you just 'cd' into the directory 'etc/uams' within the sources and type 'make' (you don't need the rest of netatalk as you already got it via 'apt-get'). The resulting UAMs can be found in the 'etc/uams/.lib'-directory - I didn't try a 'make install' as I'm not sure if I set up those paths/prefixes correctly, so I copied them over by hand.
They need to be installed in '/usr/lib/netatalk/'. When you put them there you need to set up a symlink for 'uams_dhx.so' (like the one for 'uams_clrtxt.so' already there), I chose 'uams_dhx_pam.so'.
This is working quite well here, I get about 4MB/sec. from my PowerBook to my LinkStation (both on the same switch) using a MPEG2 transport stream of ca. 3GB. It gives me a cpu load of ca. 70% to 80% on the LinkStation.