That's where it should show up. Select a portion of audio, then go to the Bounce to Disk options. Details in the Pro Tools Reference Guide->Chapter 29: Mixdown.
It is possible that the MP3.dll could have been corrupted. To rule that out, delete all files from your Codecs/MP3 folder and reinstall MP3 Option from your 6.9 CD. If you are on Tiger, install it from the Pro Tools 6.9.2 web update.
If that still does not work, then try deleting your preferences per the instructions in the " OS X/Pro Tools 6.x Setup & General Troubleshooting" topic:
http://duc.digidesign.com/showflat.php?&Number=177661