In SharePoint 2007 by default a Document Library doesn’t force checking out the document either. When you click on a document, you’ll get a pop-up asking if you want to open the document in read-only mode, or if you want to make changes.
But the good news is that you can make the check-out required before being able to edit a document. It’s very easy to do so, just navigate to the versioning settings page of the document library and set Require Check Out property to Yes.
When a user now clicks on a document, another pop-up will show where can be specified to open the document in read-only mode or to check out and edit. When the user chooses to edit the document, optionally he can specify to make the document available offline.
From the dropdown attached to a document, the user can also choose to edit in Word …
… which will bring the following pop up. So; forced check out: yet another SharePoint relief!