SBS2003 Monitoring and Reporting login error

[jamesbird]

I've a new built sbs2003 SP2 machine which seems fine EXCEPT when I try open Monitoring and Reporting in system manager I get presented with a 'connect to server.domain.local' login prompt. I'm loged into a RDT session using the administrator account on the domain, but which ever combination of server.domain.local\administrator and PW I use I cannot get in. If I cancel the login I get to a '403 page cant be displayed' window, close the window and I can see the event logs!
I guess therefore this is a intranet config problem, rather than a Monitoring and Reporting problem, but I'd like to sort it.
Any ideas you clever people?
Thanks
James