Yes. If you understand basic HTML/JS, you should understand that code at least a little.
If you want to disable say, 60" and 70" when you click LCD, then on this part:
Code:
case 'LCD':
document.getElementById('40').disabled = false;
document.getElementById('50').disabled = false;
document.getElementById('60').disabled = false;
document.getElementById('70').disabled = true;
break;
Change document.getElementById('60').disabled = false; to true.
If you want to add more TV types, just add them the same way I did, and then add a new case in the Javascript. Note that you'll have to tell all the other sizes to be true/false every time, because say you click LCD which disables 70", then you click Plasma, the 70" will still be disabled...so you have to turn it back on under the Plasma case.