It all depends on quality. I had my desktop hooked up to my tv using VGA and i can push 1920x1080 out the port so it shows up on the tv as 1080p. If your TV has a VGA input, just get a cable and setup the monitor. If you are using something like S-Video, then you might see some quality issues. Its also all about what you are downloading too. A hd dvd download rip is going to showup a lot nicer than a camera recorded movie.
“HD” Is just the resolution. Standard tv has a video height of 420px. If you are watching something in HD, its just using a higher resolution. Again, if you download a movie that is say 400px x 300px, its gonna get stretched to whatever your tv is. If you are downloading hddvd rips that are ripped and have the resolution of HD (stated above) then you will see them on your tv in “hd”