How do I customize the screen size when my TV is my monitor?

hdtvs use 1280x720 or 1920x1080

sounds like a scaling issue and its nothing serious. Depending on what card you have (ati/nvidia/intel) you need to open the control panel/control center for the video card then look for something called scaling under display properties (or something similar to that) and set the scaling lower or higher.

When you say too big and too small, do you mean the projected PC screen is overflowing (like only part of Windows desktop is projected) and miniaturized Windows desktop is in the middle of TV display with black edges?

Or are you talking about the font and icon size?

no im not talking about the font and icon size

if you have black borders between the edges of your tv and your actual windows workspace then you have a scaling issue.
your picture looks like this right?


what is the make of your video card? there is an option for "scaling" somewhere in the video card properties that needs to be adjusted (in your case, scaling you need to be increased to make the image "stretch/fill" your entire tv) make sense?

found these instructions for ati/intel/nvidia video cards

ati
http://www.hack7mc.com/2010/05/ati-gpu-scaling-removing...

intel
http://communities.intel.com/thread/26843

nvidia
http://forums.nvidia.com/index.php?showtopic=221337
at the last step you might have to check "enable desktop resizing" and then click resize
that will place 4 arrows in the corners of your screen and allow you to drag them into a perfect position to fill/fit your tv