You can add the reference to your project as follows:
1) Copy the IntelliSMSDotNet.dll to your projects 'bin' directory
2) Right click on 'References' and select 'Add Reference...'
3) Staying on the '.Net' tab click 'Browse...'
4) Select the IntelliSMSDotNet.dll (located in the 'bin' directory)
5) Click 'OK'