I 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.comYou 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>";
Data can come from a XML file, TEXT file or from flash itself.