where can i find the Microsoft.Office.Project.Schema assembly? (20

[עמרי]

hi,
when i try to work on Microsoft.Office.Project.Server.Schema.ProjectDataSet
that i get this eror:
The type 'Microsoft.Office.Project.Server.Schema.ProjectDataSet' is defined
in an assembly that is not referenced. You must add a reference to assembly
'Microsoft.Office.Project.Schema, Version=12.0.0.0, Culture=neutral,
PublicKeyToken=71e9bce111e9429c'.

and this one:

Cannot implicitly convert type
'Microsoft.Office.Project.Server.Schema.ProjectDataSet' to
'SetProjectCategoryService.Avivra04_ProjectServerDev_Project.ProjectDataSet'
so i need to add reference to Microsoft.Office.Project.Schema assembly, but
i can't find it...

Thanks,
Omri