You can download and install Yahoo! Messenger with Voice 8 from Yahoo!. However, Yahoo! forces you in such a way that you need to download a small setup program installer that will later initiate the download, setup and installation of actually Yahoo! Messenger setup file. It is hard for dialup users to download the file and all the data is lost if the disconnection occurs.
You can download full standalone setup installer for Yahoo! Messenger with Voice 8 from here (10MB+). This way you can download the file using any download manager and you dont have to download the whole file again if disconnection occurs.