First of all, I installed the hardware into my CentOS 5 machine. Then, I replaced my ivtv-kmdl package, which does not work together with DVB, with the linuxtv-dvb-apps, video4linux-kmdl and video4linux-ivtv-kmdl RPMs, all from ATrpms.net. After a reboot, the card was automatically detected. Great!

The next step was to manually scan for channels to see if it worked. Using a lot of Googling, I assembled the following command:
/usr/bin/scan -t 1 -A 2 -n /usr/share/dvb/dvb-c/nl-Casema > /root/.czap/channels.conf
This checks for all TV channels (-t 1), using cable (-A 2) and checks for NIT-other (-n). The last option is required specifically for Ziggo. The file nl-Casema is supplied by the linuxtv-dvb-apps rpm and supplies all parameters required for the scanning old Casema network (now part of Ziggo). The scan detected all channels immediately, 138 tv channels. I'm not using radio in MythTV, so I skipped detection for those.

Next was to try and tune to a channel, using one of the channels detected. I used this: czap -a 0 "Nederland 1". This will not only tune, but will also show signal strength, signal-to-noise ratio and block-error rate. In the past I've done the calculations for my tv cables and used high quality cables to ensure good quality in the attic where my tv is. This paid off:
status SCVYL | signal 8484 | snr f4f4 | ber 0000000a | unc 00000000 | FE_HAS_LOCK
The signal-to-noise ratio is very high and the block-error rate is nearly 0. Of course 0 would be ideal, but apparently that's almost impossible to achieve. As long as the unc (uncorrected block errors) stays on 0 - there won't be any issues in the recording.

The next step was to actually try and record from a channel. As at the moment, I can only read unencrypted channels, my options for recording were limited to two channels, "Nederland 1" or "Zenderoverzicht". I used gnutv (also from linuxtv-dvb-apps) for this purpose:
gnutv -channels /root/.czap/channels.conf -out file /media/mythtv/test.mpg -timeout 60 "Nederland 1"
Using frontend "Philips TDA10021 DVB-C", type DVB-C
status SCVYL | signal 7d7d | snr f4f4 | ber 0000000a | unc 00000045 | FE_HAS_LOCK

However, no matter what I tried, it just would not record. The resulting file was too small and not playable. Ultimately, the problem turned out to be with gnutv. I've never managed to resolve the issue. Instead, I switched to using czap for recording, using the following command. In one terminal I run the following:
[root@wodan .czap]# czap -r "Nederland 1"
using '/dev/dvb/adapter0/frontend0' and '/dev/dvb/adapter0/demux0'
reading channels from file '/root/.czap/channels.conf'
95 Nederland 1:388000000:INVERSION_AUTO:6875000:FEC_NONE:QAM_64:88:89:8004
95 Nederland 1: f 388000000, s 6875000, i 2, fec 0, qam 3, v 0x58, a 0x59
status 1f | signal 7d7d | snr f4f4 | ber 00000032 | unc 00000057 | FE_HAS_LOCK

In another terminal window, I then run:
cp /dev/dvb/adapter0/dvr0 /tmp/recording.mpg
This resulted in a playable file. So, the adapter is setup and working!