Ok, thx to all,
now I run kernel 2.4.23 with dvb modules.
This works fine so far with szap -r -n channel and mplayer - < /dev/dvb/adapter0/dvr0 or mplayer --dvb /dev/dvb/adapter0/dvr0, but when I use mplayer with mplayer dvb:// mplayer is losing the dvb stream and shuts down. I can watch a program for some seconds. I do not really know, what causes that, because when I installed the modules I could use mplayer dvb:// without any problems. Now, after reboot, it does not work any longer.
It seems that the frontend or demuxer times out and can't be kept alive by mplayer or something like this.