What happens when you enter snip in Start/Search and hit the Enter key?
If nothing then you may have inadvertently turned off the optional Tablet PC features, of which Snipping Tool is one (since 2005).
- Click on Start button, and go to Control Panel.
- Click on Programs link then Programs and Features.
- Click on Turn Windows features on or off link. If User Account Control pops up for confirmation, click on Continue button.
- Scroll down the list of features in Windows Features dialog window, tick the check box for Tablet-PC Optional Components to enable and show the Snipping Tool
Then it should show up under Start/All Programs/Accessories.
Going by memory here as I'm in Vista right now.