1. way
create file:

Windows Registry Editor Version 5.00



without lines. Save it as disable.reg
(All files, then name it disable.reg )

Start it.

-restart or log off from PC.


2. way

-navigate to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
-right click in the right panel.
-New/DWORD Value
-name it "EnableBalloonTips", without quotes
-double clik it, set value to 0
-restart or log off from PC.

source: http://support.microsoft.com/kb/307729