If you are using cable you can get the HDHOMERUN QAM tuner it will probably on get your lcoals in hd
Or you could get a local OTA hdtv tuner from avermedia M780 I belive is the current model.
Only option to get unecrypted hd channels from CAble currenty is purchase a new PC with cabe card.
Dell xps420 w/ dual ATI cable cards
Hdhomerun for QAM
Panasonic 50" Plasma fed by xbox 360
Panasonic 42" plama fed by xbox 360
3TB in storage and counting