VS 2005 Team System integration with Visual Studio currently does not always get the latest version of a file when you begin editing it. This has been an annoyance for many including me. This paradigm is so different from the hard core Source Safe developers way of thinking that the the next version will provide a configuration setting for developers to decide on to get the latest version from source safe and risk breaking code.
Here is an article about how it currently works: http://blogs.msdn.com/buckh/archive/2005/08/20/454140.aspx
In VS 2008 (currently code name Rosario) you will be able to configure how files are checked out. Here is a link to new features. http://msdn2.microsoft.com/en-us/teamsystem/bb407307.aspx