How to test for this when I don't know what the users computer will have installed and what it defaults to? How do I see this result if I have the font installed?
DER moment, just drag that font your dynamic text field is using out of your (on a mac) System > Library > fonts folder and anywhere else it is installed. (search for the font name in spotlight). Drag the font file onto your desktop or something and your computer will think that the font isn't installed. Then test your projector (built before 'uninstalling' the font of course), and low and behold, if you havn't got your fonts embedded in your projector, you will see the default font, which is Times. This will very clearly show you if your fonts are embedded in every dynamic text box instance in your project. (you need to click the properties panel 'embed button' for every text field on stage, or do it via actionscript and adding the font to the library. If you don't see Times font with your font 'unistalled', then your fonts are embedded properly, to test try on one dynamic text field clicking the 'embed' button and clicking 'unembed', then publishing your projector.
If you don't drag the font out of your system fonts folder to test this and your fonts are not embedded properly in the flash projector, the dynamic text field will use the intended system font if its available to render the text, which actually looks very similar, but different (heavier) to what the font looks like when its embedded properly in the flash file. Without an eagle eye you might not notice this. But your end user certainly will if they don't have that font and see the dreaded Times instead! If your using a dynamic text field in Flash, embedding the font of choice is essential (unless you need a really small file size for the web delivery and don't care about font consistency).
A really helpful resource to learn about text in Flash is called "Foundation Flash CS3 for Designers" By Tom Green and David Stiller and Friends of ED. Chapter 6 "Text in Flash CS3" explains almost everything you need to know about fonts, embedding, aliasing etc.