I asked the same question on Stackoverflow - how do i add reference to external resource dictionary and have it show up on my blend resource panel?
To link to an item...
Project > Link To Existing Item > (Navigate to the external Resource Dictionary, select it and click ok.)
Just know that any changes you make in the linked, you are making in the original.
Microsoft is conducting an online survey to understand your opinion of the Msdn Web site. If you choose to participate, the online survey will be presented to you when you leave the Msdn Web site.
Would you like to participate?