Multiple VS.NET projects and CVS common sub directories

VS .NET allows to isolate binding with SourceControl (CVS) based on
the project level. I.e. theoretically each project can be connected to
its own SourceControl server and path (CVSROOT and module).
However, by default, when you add entire solution to SourceControl, VS
.NET, without any prompts add entire solution and all sub projects
under the same module tree into repository. You can change this
behavior if will add solution to CVS project by project. This way you
will be able to specify for each project it's own source control
binding.
Later, when you will need to "reuse" some project in other solution
you can use "Add from source control" command, which will allow to add
project from any server location (that can be not part of solution
module).
Please only note that SourceControl granularity term is Project. You
cannot share same way single files or directories, only projects.
Let me know if this answer to your question.