I suggest you uninstall the version of MediaPortal that you have, delete the Mediaportal folder, and then install version 0.2RC4, which you can get from
here. Don't be concerned that it is called a "test release" - I have found it to be very solid and stable.
Run configuration again, and autotune - if you still have no joy, let us know if you have a choice of more than one card in the drop-down box, and what those names are - I think you should only find "DNTV Live! Pro Transport Stream Capture", as I don't think the analogue section is supported in RC4....I could be wrong though!
It would also be helpful if you posted your MediaPortal.log file information (Please use
http://mp.pastebin.com and then post the link in your forum thread), if you still require assistance.