By default, Windows 7 keeps the Windows Live Messenger icon on the Taskbar instead of moving to the system tray. If you want it off of your Taskbar so that it behaves like it did before, you can easily place it on the system tray, giving you more room on your Taskbar for other applications and files.
1. Close Windows Live Messenger.
2. Open Computer and navigate to:
C:\Program Files\Windows Live\Messenger
or For those that have 64-bit the path is "C:\Program Files (x86)\Windows Live\Messenger"
3. Right-click on msnmsgr.exe and select Properties.
4. Select the Compatibility tab.
5. Go to the Compatibility mode section and check the Run this program in compatibility mode for checkbox.
6. Use the dropdown and select Windows Vista.
7. Click OK.
Now when your chat client is active, but not in use, you will find it in the system tray