Windows Messenger was an instant messaging client from Microsoft which could connect to Microsoft .NET Passport (now Windows Live ID), SIP (session initiation protocol) communication services, and Microsoft Exchange Instant Messaging. Windows Messenger 5.1 was included with Windows XP but was not released for any newer versions of Windows (it has been replaced by newer products like Windows Live Messenger and Office Communicator). You can obtain more information about Windows Messenger from the Windows Messenger How-To Center on Microsoft’s web site.
Windows Messenger is fairly out-dated and does not have many of the features included in newer versions of MSN Messenger/Windows Live Messenger (see this Microsoft document for some details). It can still can be useful (or even necessary) for some things. It is especially handy because it works alongside MSN Messenger/Windows Live Messenger and is not affected by their installations. If Windows Live Messenger is broken or unable to connect you can use Windows Messenger as a backup. Windows Live Messenger also cannot connect to SIP communication services or Exchange instant messaging.
You can download the installer for Windows Messenger 5.1.0701 from here.
When you run the “Messenger.msi” installation file under Windows Vista or Windows 7 it fails partway through the installation process, reporting that the installation was interrupted. The problem is caused by a compatibility issue between the MSI package and UAC. You cannot simply adjust compatibility modes or elevated privileges for standalone MSI packages like you can for setup executables because they are handled by the Windows Installer service.
To get it to install properly, open an elevated command prompt (right click the “Command Prompt” shortcut under the start menu and select “Run as Administrator”). From the administrative command prompt enter the commands:
msiexec /a <path>
msiexec /i <path>
Where <path> is the location of the messenger.msi file. So if I saved it to my desktop, the commands would be:
msiexec /a C:\Users\Keith\Desktop\Messenger.msi
msiexec /i C:\Users\Keith\Desktop\Messenger.msi
The installation will run and should be able to complete successfully.
Keith B's Tech Blog 
[…] Messenger 5.1.0701 here. To install it under Windows Vista or Windows 7 you will need to use a workaround or disable UAC to get the messenger.msi file to install […]
i spent 3 days trying to get the new Office Communications Server 2007 to work, it is the absolutely worst product by Microsoft, bugs after bugs on install and tons of work around. I am so glad I found your tip on running this on W7. OCS is the biggest piece of shit ever.
Thanks so much! Tried getting it to run in Windows XP Mode and although it worked, it was not as seamless as running it this way. Cheers!
BRILLIANT
Hello. Do you know how fix the bug in Windows Messenger in Windows 7 that Freeze the Messenge when the dialog box be full ?
thanks
I have got Windows XP and it had Windows Messenger 4.7 as it came with Windows XP. But I uninstalled it as it is no longer supported,it is now out of date. And if you try to log in with 4.7 and 5.1 you get an error message, telling you to upgrade to the latest version of Windows Live Messenger. So you cannot run Windows Messenger 4.7 or 5.1 on any version of Windows now,not even XP. As I tried and it does not work.Andrea Borman.
Install Windows Messenger 5.1 on Windows Vista or Windows 7,
Thanks very much!!!! Your instructions worked perfectly and were very easy to follow.
I managed to get 5.1 working on Windows 7 under compatibly mode for windows 2000
Thank you very very much, works perfect in windows 7.
I hate Windows live essential, also i dont like windows 7.
Windows Messenger 4.7(from XP)never worked on Windows 7.When I tried 5.1 it did and it also works on EWindows 8. Though I never had to enter any comand to get it working.I just run it in program compatibility mode for Windows XP. but Yes it works on Windows 8 and I am going to try it on Windows 8.1.
Ellen.
[…] Messenger 5.1.0701 here. To install it under Windows Vista or Windows 7 you will need to use a workaround or disable UAC to get the messenger.msi file to install […]