i have three VS solutions :
Human-resource Solution
Payroll Solution
And a Main web site (Shell);
Human-resource is a solution which is also a
Yep, go to File->Source Control->Add Project from Source Control...
This will pop up a dialog allowing you to add a project from elsewhere in source control.
Once you get into sharing projects like this, it's worthwhile getting a bit robust in your source control structure, so this is worth a read:
http://tfsbranchingguideiii.codeplex.com/wikipage