Hallo!
I wonder if anyone did vowel recognition with Pd.
AFAIK no.
I added speech recognition for the GSoC projects some day ago: http://puredata.info/dev/summer-of-code/SpeechRecognitionForPD
So you could try to use SPHINX or HTK. E.g. look at this tutorial: http://www.speech.cs.cmu.edu/sphinx/tutorial.html.
LG Georg