I used to run a mythtv server a year or so back. I haven't touched tvheadend. So someone else would be of more help. But there seemed to be a general order in getting dvr software setup.
Typically it goes like
Install card/drivers -> install software -> Configure software.
Setup card in software -> scan for channels -> Set up electronic program guide -> choose storage point -> set up what you want to record.
The DVR software generally needs electronic program guide data, Mediacenter has this pretty much built in. For linux last I checked schedules direct was the primary EPG service. Looking on tvheadends site xmltv is referenced quite a bit. It seems like it also offers data, not 100% sure see
http://wiki.xmltv.org/index.php/XMLTVProject
I'd think. it would be something like this in the web front end.
Click on configuration
Go to DVB adapters, add the card. If not there.
Go to xml tv, select your data location(country), select interval etc.
Go to channels. Auto scan, make sure they match up with your area?
That should be a start.
Have you verified that you can play TV with the card under nix? Easiest way if i remember is using mplayer. Which was something along the lines of mplayer /dev/dvb/{blah}
http://www.linuxtv.org/wiki/index.php/MPlayer
The ^ above should only be necessary as a later troubleshooting method.