How to link multiple visual studio solutions together?

Question

I have 3 solutions and solution A requires built versions of the dlls from solution B and C in order to compile. it is not possible to merge it to one solution...

So far

Answer 1

I have recently discovered that in Visual Studio 2008 you can include existing projects in multiple solutions. The only downside so far seems to be that if you make a change to a shared project and have multiple solutions open that use that shared project you will be asked to "reload" the other solutions.

So, just "Add Existing Project" to all the solutions that need the project. I am using TFS on my current site and there seems to be no issues with source control ether.