Installing MS Exchange 2003

Anyone out there had problems installing Exchange 2003?
I have run forestprep and domainprep but I still get an unknown error message 0xc0070051 (81) when I try to run setup and choose typical from the Action tab.
I get “Microsoft Exchange has a unknown installation problem” when I choose custom install.
In the installation log one of the first error messages is:
ANONYMOUS LOGON does not have READ permissions for MDB objects on the organization
The required permissions have not already been set

What does this mean?
LOST
Charlie