Microsoft.office.core

I have a .net project and I added a reference to Microsoft office 12.0 Object Library.  It added Microsoft.Office.Core to the references but it has a warning symbol that it can't be found.

OK.  I installed the Office 2007 PIAs and now have Microsoft.Office.Core , Microsoft.Office.Core and VBIDE  all of which have a warning symbol and when I build i get erros that none of them can be found.  If I look in Windows\assembly, Microsoft.Office.Core is there.

How do I resolve this?

Thanks