At the Kent partner group I was asked if shadow copies applied to all volumes or just the main system volume.  To find out the answer I typed "vssadmin list shadowstorage" and the result was:

C:\Windows\system32>vssadmin list shadowstorage
vssadmin 1.1 - Volume Shadow Copy Service administrative command-line tool
(C) Copyright 2001-2005 Microsoft Corp.

Shadow Copy Storage association
For volume: (C:)\\?\Volume{f2dea953-2674-11db-b0e9-806e6f6e6963}\
Shadow Copy Storage volume: (C:)\\?\Volume{f2dea953-2674-11db-b0e9-806e6f6e6963}\
Used Shadow Copy Storage space: 5.622 GB
Allocated Shadow Copy Storage space: 5.874 GB
Maximum Shadow Copy Storage space: 6.05 GB

Shadow Copy Storage association
For volume: (E:)\\?\Volume{f2dea955-2674-11db-b0e9-806e6f6e6963}\
Shadow Copy Storage volume: (E:)\\?\Volume{f2dea955-2674-11db-b0e9-806e6f6e6963}\
Used Shadow Copy Storage space: 33.453 MB
Allocated Shadow Copy Storage space: 300 MB
Maximum Shadow Copy Storage space: 961.343 MB

This tells me how much storage is used on each disk and whether it is enabled.

Vssadmin does much more (the Server 2003 information can be found at http://technet2.microsoft.com/WindowsServer/en/library/89d2e411-6977-4808-9ad5-476c9eaecaa51033.mspx?mfr=true

You can also control the amount of space used etc using this command too.