The big snapshot button is gone from v6.24 onwards, but you can still take snapshots in a few different ways:
1) You can press F11. This takes a snapshot of the sequence, not the clip preview.
2) You can right click the clip preview and select Take Snapshot of Clip. This should take a snapshot of the clip preview.
3) You can use File menu -> Clip -> New Freeze Frame Image from Preview or File menu -> Sequence -> New Freeze Frame Image from Preview.