Windows Server 2003 SP1 Support Tools.
Since we all use many of these support tools for Exchange, it is interesting to note that SP1 includes an update to many of the old tools we use, like:

LDP.exe
ADSIEdit.msc
NetDiag.exe
and others...

The supported operating system in Windows Server 2003, but it can be installed on Windows XP as well.
You can download them here:
Download SP1 Support Tools

Oh...  and of course SP1 is out as well.  Look for more information on how to deploy the SCW and more with Exchange from the people at "You Had Me At EHLO..."  I got word in advance that they sould be writing about it, so keep an eye out for it.