UPDATE: This method no longer works in newer versions.
Did you know there is an extra hidden tab in Windows Live Messenger Option dialog box? Its called "Add-ins". Its hidden by default. But there is a registry hack available to enable it.

Here is a step-by-step tutorial to enable it:
1. Type regedit in RUN dialog box and press Enter. Now goto:
HKEY_CURRENT_USER\Software\Microsoft\MSNMessenger
2. In right-side pane, create a new DWORD value and give it name "AddInFeatureEnabled" and set its value to 1
3. That's it. Now open Windows Live Messenger and go to "Tools -> Options" and you'll see a new tab "Add-ins".
This article was posted by VG in following section: Windows Live.
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blue
The key was already in the registry when I got there to create it - also enabled - but no add-in tab in messenger!
Using Windows Live Messenger version 2009, build 14.0.8064.206.
coredump
This seems to have changed with the new messenger. I had an add in running in the previous version, it ran fine.
After i upgrade the add in isn't enabled any more and the add-ins option has disapeared from the menu. Some how this new messenger uses an other variable to allow use of the add-in. That is if this option is still available in this version.
I search the ms developers sites, but at this point there is no reference to anything that might be a solution to this case.
Mike
I noticed the same problem and still have not found a workarround
Greer
Hey, I go onto regedit and then i cant find this tab on the right hand menu..
HKEY_CURRENT_USER\Software\Microsoft\MSNMessenger
Not sure what to do now..
Can you help?
Thanks :)
JK
anyone found a solution to this for Messenger version 2009?
Eran
It didn't work I actually had that Dword Value n there and it was set to 1 but still its not showing up the add in tab! )o:
Mike
To everyone - this does not work in 2009 windows live mesenger!!!!
A solution has not yet been found !!!
Pepper
I don't know if it matters, but I'm on XP and it didn't add the Add-ins tab. Any suggestions?
aelien
didn't work
John Doe
It doesn't work for the newer versions of windows live :-(