You must link to the same file from both projects.
Try this:
1. Start a new project (or use one of your existing ones)
2. Create a new Module and call it LinkText.vb
3. Add a Function to it, and save it.
4. Start a new project (or use a different one that already exists)
5. Right click the solution in the Solution Explorer
6. Select Add > Existing Item...
7. Find and highlight the file you want to LINK to
8. Click the Down-Arrow-Carrot that is on the right of the ADD button.
9. Select "Add as Link"
You can see that the icon for the file you just added has a shortcut indicator in it. That means that this file is added as a link. Changes made in the file here affect the file in your other project.
I hope this helps.
http://msdn.microsoft.com/en-us/library/9f4t9t92.aspx (scroll down some, add existing item as a link)
-Sean Campbell