Maybe you have already seen that in some Visual Studio 2005 projects : a item that represents a link to a file (see image below).
It is very handy to reference through a link a file : for example, if you have three projects that uses the same file, just put a link. But when I add item to my project, I cannot see a Link or a similar option. This is because it is a bit after. Here are the steps :
1) Go to the Solution Explorer
2) Select "Add an Existing Item"
3) Select the file to add and click on the arrow at the right of the button "Add", and click on "Add as Link"
4) In Solution Explorer, you see the linked file