Before digging deeper into the Multiple Check-Out Model, it's very important to state the following note:
Multiple checkouts are available by default only for files that contain plain text—text files. Binary files cannot be checked out by multiple users and they will always behave as in the exclusive mode. This is because binary files cannot be merged using default text file tools. However, custom merge tools can be configured for text and binary files as well. For more information please refer to the additional material provided online at http://www.packtpub.com/visual-sourcesafe-2005/book.
To begin using the Multiple Check-Out Model, it must first be activated.
In Visual SourceSafe 2005 the check-out model ...