I want just want to share with you the way I get may subscript and superscript inin dynamic and input text field in Flash:
<sub> & <sup> tags are not supported by Flash but you can
use Subscript & Superscript in dynamic and input text field in Flash:

Download & install Subscript & Superscript fonts from http://www.subscriptfont.com or http://www.superscriptfont.com
You will need to restart Flash software after installed fonts.
Create a dynamic text field with Arial font embeded. Set the HTML property to true.
Create a dynamic text field with Subscript font embeded.
Create a dynamic text field with Superscript font embeded.
Use HTML tag to set text to subscript or superscript like below:
Some text<font face="Superscript"></font>
If you are using ActionScript to test the htmlText, use script like below:
my_txt.htmlText = "Some text<font face='Superscript'>TM</font>";

They are better than CG since it goes lower than the baseline and it's real subscript..