When I build from the trunk I usually follow the instructions found here:

http://using.castleproject.org/display/CASTLE/Using+the+Trunk

My source location is slightly different from the instructions so I have to hand edit the registry entries listed at the end of the page. So to save me doing that again here they are:

Windows Registry Editor Version 5.00 [HKEY_LOCAL_MACHINE\SOFTWARE\Castle] "vs8templatelocation"="C:\\source\\Castle\\Tools\\VSNetWizards\\CastleTemplates\\VS8" [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\v2.0.50727\AssemblyFoldersEx\castle] @="C:\\source\\Castle\\build\\net-2.0\\debug"