Windows snapshots and VMware snapshots are two completly different things.
Windows snapshots are created from within the Windows operating system.
The Windows Volume Shadow Copy Service (VSS) only came into existence from Windows XP onwards. If you are looking to create a Windows based snapshot of WIndows XP and later, then VSS is what you would use.
VSS is not available in Windows NT but I am not to sure if Windows offered another way of creating Windows snapshots in the NT operating system?
A VMware snapshot is a different ball-game altogether. VMware offers the ability to take a snapshot of the virtual machine (not related to guest operating system inside of the VM).
A VMware snapshot preserves the state and data of a virtual machine at a specific point in time. It creates a whole new VMDK called a delta disk and while the snapshot is present, the virtual machine then runs off that new snapshot disk as opposed to the original VMDK. While a snapshot is present, all new disk changes are written to the delta disk, and as a result the delta disk can grow/expand in size.
For information relating to VMware snapshots, see the following articles in our Knowledge Base:
http://kb.vmware.com/kb/1025279
http://kb.vmware.com/kb/1009402
http://kb.vmware.com/kb/1015180
http://kb.vmware.com/kb/1007849
Some of these articles contain useful KB videos as well.
Hope these help you!