How to properly format text in sheet on OS X?

[Brian K. Maher]

Hi Folks,

I am trying to properly format the text in an 'answer ... as sheet' 
command.  I need to message text to conform to OS X's UI guidelines 
which state that the 'message text' should use the emphasized bold 
system font and the 'informative text' should use the small system 
font.  Below is my command so far but the fonts don't seem to be 
working:

answer warning "<font face='Lucida Grande' size='13'><b>message 
text</b><br><br></font><font face='Lucida Grande' size='11'>informative 
text</font>" with "Continue" as sheet

Can anyone help me get this working properly?

Thanks, Brian