What OS is installed on that PC?
If that PC came with the tuner, then you likely already have the necessary software.
As denyasis hinted at, if you're running Windows (XP) Media Center 2005, 2004, or 2002; or Vista Home Premium, Vista Ultimate, then the software (Media Center) is already there.
Most all TV apps (MC included) record to mpeg2, because most tuner cards handle (in hardware) the compression. Media Center records in .dvr-ms (which is simply mpeg2 in an asf wrapper, to allow metadata to be encoded into the file.)