I can not download yahoo 9.0

check the firewall settings of your server/administrator. the application download has been blocked for security and other purposes.

if they won't allow you to, try to download it with other servers that have no restrictions.

I run Vista with Messenger 9
The old Messenger folder probably failed to fully uninstall
When downloading/uploading close all other programs. I suggest you download and run ccleaner first before you proceed further. Run it through a couple of times - include "registry" from the left hand toolbar. Do not be alarmed at the amount of files you have to delete, especially if you do not clear it on a daily basis. Use this path to uninstall and remove the old messenger software.
> Start > Computer >> Local disk (C) >> Program files >> Yahoo >> Messenger
If the uninstall was successful, and you have Vista, the Messenger folder should not be seen.
If you have Vista, so you can safely delete the Messenger folder
If you have a pre - Vista OS, preserve the Messenger folder and the Profile sub-folder inside ( It contains the Archives ) Delete anything else inside the Messenger folder
Delete shortcut on desktop
Restart computer

http://www.filehippo.com/download_ccleaner/

http://www.filehippo.com/download_yahoo_messenger/