I believe I have the EXACT same TV as you: the Samsung HLS-6187W 61" 1080p set? I too am getting DishHD Silver installed tomorrow (or later today since it's past midnight). Your TV is capable of inputting a 1080p signal; however, as Tom said, no HD TV stations currently broadcast or have any plans of broadcasting in 1080p. Your TV is, however, great for such things as a 1080p upconverting DVD player (such as the Samsung HD-960, which takes your regular 480i natively-encoded DVDs and upconverts them to 1080p by "filling in" missing pixels intelligently), a SECOND-generation HD-DVD player with content natively encoded in 1080p (not out yet but should be before year's end - first-generation players are out now but only output in 1080i even though the disc is encoded in 1080p), a Blu-Ray player that also natively outputs 1080p content (out June 25th), or a PS3 which has some 1080p games and will be out November 17th. This effectively "future-proofs" your TV, and while the broadcasters aren't changing anytime soon, I'm sure you will be blown away by a Blu-Ray video disc over HDMI seen its full glory.
No, you do not have to change anything in your TV to view broadcasts in the correct resolution - your TV will do this for you and, (at least when watching OTA HD - all I can vouch for at the moment), a thin bar at the top of your screen tells your whether the channel is outputting in 720p or 1080i.
Finally, in general HDMI WILL look better than component cables (since HDMI=digital and component=analog), so I suggest you get a GREAT and CHEAP HDMI/HDMI cable from Monoprice.com and hook up your amazing TV with amazing cables. One cable costs $5.97 and you can get two for $4.97 each (that's what I picked). Here's the link:
http://www.monoprice.com/products/p...=10240&cs_id=1024004&p_id=2412&seq=1&format=2
And yes, these cables will perform JUST AS WELL as those $125 Monster gimmick cables. If you have any more questions, just ask! And head on over to
http://www.avsforum.com if you wish to become more enlightened on this subject or any subject HD or tech-related!