Yes you need a HD Satellite receiver to watch HD Satellite.
The main reason why your TV has a tuner in it is because the FCC mandated that 50% of TV's over 36" have to have a built in tuner by July of 2004.
A built in tuner is good thing to have. For one you can watch OTA HD with just an antenna without any additional equipment. Although you may never use this is it is nice to have the option.
But more importantly your TV has a built in MPEG2 decoder and although you didn't post your model number so I can't confirm this I would bet your TV has a Firewire port (sony calls it iLink). This will allow you to someday network all your equipment with less wires, and add integration between your components. This may also allow you to purchase cheaper HD equipment since you will be able to buy components without their own MPEG2 decoder since you already have one.
See this link
http://www.mitsubishi-tv.com/networking.html
The main reason why your TV has a tuner in it is because the FCC mandated that 50% of TV's over 36" have to have a built in tuner by July of 2004.
A built in tuner is good thing to have. For one you can watch OTA HD with just an antenna without any additional equipment. Although you may never use this is it is nice to have the option.
But more importantly your TV has a built in MPEG2 decoder and although you didn't post your model number so I can't confirm this I would bet your TV has a Firewire port (sony calls it iLink). This will allow you to someday network all your equipment with less wires, and add integration between your components. This may also allow you to purchase cheaper HD equipment since you will be able to buy components without their own MPEG2 decoder since you already have one.
See this link
http://www.mitsubishi-tv.com/networking.html