There used to be a registry entry that we used in XP/Vista to enable/disable balloon pop ups, don't know if it would work in win 7
Method 1
Click Start, Run and type Regedit.exe
Navigate to the following subkey:
HKEY_CURRENT_USER \ Software \ Microsoft \ Windows \ CurrentVersion \ Explorer \ Advanced
Create a new REG_DWORD (32 bit) value named EnableBalloonTips
Double-click EnableBalloonTips, and then assign a value data of 0
Exit the Registry Editor
Log off Windows, and then log back on.
Method 2
Click Start and type GPEDIT.MSC
Navigate to:
User Configuration \ Administrative Templates \ Start Menu and Taskbar
Double-click Turn off all balloon notifications and set it to Enabled
Close Group Policy Editor
Log off Windows, and then log back on.