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. This is troublesome for those IM lovers who don’t have always-on Internet access, or have slow Internet connection speed, or want to offline install, or want to network install, or simply want to keep the binary for future installation, or for whatever other reasons.
Whatever reason you have, you can download full standalone setup installer for Yahoo! Messenger with Voice 8 (currently at version 8.0.0.683): ymsgr8us.exe (about > 9 MB, should be the general link that download the latest series in version 8 – no longer available) or ymsgr800_683_us.exe (version 8.0.0.683 – no longer available) or ymsgr810_195_us.exe (version 8.1.0.195 – no longer available).
If you install Yahoo! Messenger with Voice by using the small loader setup file, you can find the full setup file at C:\Program Files\Yahoo!\Installs (assuming you install using default folder destination), as YM8 setup file is downloaded temporarily here for installation. However, the full installation file will be deleted once installation is completed. So you need to get the installer during the installation.
Update: Latest version 8.1.0.413 of Yahoo! Messenger.