What are the Differences Between System Restore and Snapshot ?

I assume you are talking about Windows System restore and VMWARE snapshot.System Restore helps you restore your computer's system files to an earlier point in time. It's a way to undo system changes to your computer without affecting your personal files, such as e‑mail, documents, or photos. It's designed to take the system state back not to roll back the entire system.VM snapshots take the machine back to precisely how it was. They are the equivalent to taking an incremental image backup.

A snapshot is a set of data and configurations that a system contained in a given moment in time

A system recovery is a process that is meant to reverse a system from its current set of data and configurations to the ones it had in a previous snapshot

well the SS is mostly used as testing and working on a specific task accurately and controllably because SS work on a single change task so you can creates many SS and roll it back individually but system restore work on the whole system on a specific date 

I suppose that your are referring to this kind of Windows System Restore:

http://support.microsoft.com/kb/310405

(cause there is also ASR and other similar name for other functions).

This is only a way to make some checkpoint for critical files, drivers, and registry backup.

If you loose a  lot of documents or programs you cannot restore with this tool...

If you got a virus your cannot restore your system with this tool...

A snapshot of a volume is a freezed state of a volume and your can roolback to this state

Thanks :)