you need an HD signal from direct tv in order to get the HD picture that you saw in the store. coax will never do it for direct tv. svideo will not do it either rather its $10 or $200.

since you have a dvr, (i'm assuming you'd want to keep it), you're gonna need a HD box from direct tv with an HD dvr. the price is $499.99. it comes with component AND hdmi cables that you'll need to hook it up to get HD, so no need to get extra cables unless the box is 12ft+ away from the tv.

essentially, your tv has a lot of dots on the screen. you need to fill up those dots with something. directtv wont send you those extra "dots" unless you pay them money and get a box that can decode THEIR signal. unfortunately, you'll need the box no matter what HD tv u get.