I changed the screen resolution to 1280 x 720, but that was too big, then I changed it to 1024 x 768, but that was too small. Is there a way I change customize the screen resolution to somewhere in between?
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?
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
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