The Hauppauge capture cards such as the PVR-x50 cards (this includes the PVR-150 and PVR-250 cards), which have MPEG2 encoders, should be set up using the "MPEG-2" encoder option, not the Analog V4l capture card option. The setup is pretty simple, since all you have to do is select the "MPEG-2" option from the Capture Card Setup page. Earlier versions of MythTV may have an "IVTV" option but this should be eschewed in favor of the "MPEG-2" option. That's about all there is to it.
However, if you have both a PVR-x50 card and a pcHDTV card (or one of the other HDTV cards like the HD 800i) in the same box (because the analog recording with the pcHDTV card kludge doesn't work worth a darn), you may experience a collision between the two cards. Depending on the order in which they are plugged into the PCI bus, one or the other of the cards may disappear when it comes time to configure them. This can be corrected by changing /etc/modprobe.d/options (outside of backend configuration):
sudo touch /etc/modprobe.d/options
sudoedit /etc/modprobe.d/options
Add the following line (or one similar to it):
# Fix collision between pcHDTV/HD 800i and PVR-150.
options cx8800 video_nr=2 radio_nr=2
Once you've made all of your changes, you may want to reboot the system a few times to be sure that what you've done is working. One can never be too sure when the clever, little PCI bus is involved.
If you wish to test that the card is working, before you let MythTV have at it, you first need to ensure that the v4l and ivtv utilities are installed:
su
apt-get install v4l-utils
apt-get install ivtv-utils
Once you've done that, you can try the following (assuming that you're debugging the first card in the system, on /dev/video0) from a console on the primary display:
v4l2-ctl -i0 -d /dev/video0
ivtv-tune -c3 -d /dev/video0
mplayer -vf pp=lb /dev/video0
You should see a mplayer window that shows the analog program that is currently playing on channel 3, on tuner 1. If, for example, the card is cabled to the output of a cable company DTA, this should show you whatever is playing on the channel selected on the DTA.