I found this post on Yahoo Answers....it was a couple of clicks, and it works!
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"I recently upgraded to Vista and was running into the same roadblocks. Luckily I stumbled across Bytescribe's FAQ page, which has a link to an installer that takes care of the codec installation for you quickly and easily.
The FAQ page is at
http://www.bytescribe.com/support/vista.... , and you'll want to look under "Product Compatability List" in the section that mentions something called "Export Utility". There is a link there to a TrueSpeech Codec Installer .exe file on bytescribe.com's site itself that I have confirmed is a safe link.
The installer is located here:
http://www.bytescribe.com/downloads/tsp_... . Download the .exe, run it, restart Yahoo Messenger, and you should be all set."