For this tutorial we will use the Manage Content and Structure Feature in SharePoint 2007. It is a very useful browser interface that allows you to move items and yes, check in and out multiple documents. To get to this feature we will use the Site Actions Menu. Please note you must have the proper permissions (contribution at least) and you will not see all the options from the screen shots below if you do not have full control permissions.

1. On the Out of the Box SharePoint Site the Site Actions button is in the top right hand corner. Click Site Actions and Manage Content and Structure.
   
2. Navigate to the Document Library and folder containing the documents you wish to check in and click on it to expose the documents to the right.
   
3. Now if you haven’t seen this check box before it simply selects all the boxes in the view. Click this select all in view or simply check the ones you need to check in or out.
4. Highlights your selections
   
5. Now using the Actions Menu select Check In or Out depending on your task
   

Now you have successfully checked in or out multiple documents. Easy.