Thanks to wpk at irc, I’m happy
[ 5871.927366] DVB: registering new adapter (ASUS My Cinema U3100 Mini DVBT Tuner)
[ 5872.147898] DVB: registering frontend 0 (DiBcom 7000PC)...
[ 5872.324241] DiB0070: successfully identified
user. I’m using 2.6.26 kernel with udev, so I’ve to only plug the USB dongle.

The next thing is to scan the ether for digital TV networks. To do so, use w_scan utility (or compile it from SPEC). If lucky, you’ll get channels.conf for found services in your area.
In my room, I’m receiving four german channels, and four more on the balcony. Additionally, I see five polish tv channels and three radio too, but the signal is poor, so I can see nothing than only list of them.

wpk says, that as they’re coded with MPEG-4, there can be problems under linux with displaying it due to lack of MPEG-4/ H.264 support under Linux.

Next, there are two methods of tuning in. If you’re ready with your ~/.mplayer/channels.conf you can just
smplayer dvb://3sat to see live TV.
You can also tune in manually, e.g. tzap -c ~/.mplayer/channels.conf -r 3sat and run your favourite soft to see the stream, e.g. mplayer /dev/dvb/adapter0/dvr0
ffmpeg /dev/dvb/adapter0/dvr0

To see the signal status when using mplayer run femon tool. I’ve noticed, that output like that
status 1f | signal 522e | snr 0000 | ber 00068480 | unc 0000001c | FE_HAS_LOCK
status 1f | signal 531c | snr 0000 | ber 00013150 | unc 00000000 | FE_HAS_LOCK
gave great quality.
Status must have 1f, FE_HAS_LOCK is shown, ber is not 001fffff and the unc is low (or zero). The shortcuts are explained at MythTV Wiki (the description of numbers’ meaning differs with my observations of them).

The next thing is to adapt bigger antenna, aim a broadcaster and deal with mpeg-4 problems (if there’s any).