If you need to create a GUID in VS2008 but this menu is disabled then you are facing the same problem as I did. Probably some options were disabled during installation. Fortunately it is easy to fix.

Copy two files guidgen.exe and Uuidgen.Exe form
C:\Program Files\Microsoft SDKs\Windows\v6.0A\bin
to
C:\Program Files\Microsoft Visual Studio 9.0\Common7\Tools
and you don’t even need to restart your Visual Studio.

Download Community Technology Preview (CTP) of Microsoft Visual Studio 2010 and .NET Framework.

I have met this problem when I worked on some Visual Studio add-ins:
VS Add-in Wizard does all work around to insert your add-in to Visual Studio menu "Tools" but if you want to make your add-in available in other menus, let say in context menu of Solution Explorer, you have to know some additional information about the place.
To get this know you need to add Registry value DWORD EnableVSIPLogging to  HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\9.0\General and set it to "1". Then just press Ctrl+Shift and do an operation you interesting in. You will get a dialog box, similar to this:

Don't forget to switch it to "0" (zero) when you will no longer need it because Visual Studio has many commands that start from Ctrl+Shift.
It works in Visual Studio 2005 SP1 or higher.