Seems the best solution for your needs without infringing other people's copyright
Thank you Marki show some packages in http://www.lingoes.net/en/translator/speech.htm1. lingoes basic english voice package2. Longman 2005 Voice Package - American English3. Longman 2005 Voice Package - British English4. Webster Voice Package - English
But still not sure whether i can use them for my web dictionary.