This is what I use
While it is possible to disable the windows key by
modifying the registry, doing this leaves the key disabled all the time and requires a restart if you wish to change the behavior.
A better solution (if you are using Windows 2000 Service Pack 3 or Windows XP) is to use the
Windows Application Compatibility Toolkit, which you can download from Microsoft. This allows you to disable the windows key for specific applications (in this case Diablo II), while allowing the key to remain enabled for everything else.
To set this up after downloading the toolkit from Microsoft, follow the instructions on
this page. The instructions provided are for playing FFXI, but you can simply substitute
Game.exe (from your Diablo II directory) instead of Pol.exe and it'll work fine.