Windows SBS and Windows STD

I cant seem to get my Windows 2003 STD server to install AD as a secondary DC.
I tried the adprep stuff, and that says nothing needs to be done...

But when I try to install AD on the Win2k3 STD machine I get the error:
----------------------------------------------------------------------
The Active Directory Installation Wizard cannot continue because the forest is not prepared for installing Windows Server 2003. Use the Adprep command-line tool to prepare both the forest and the domain. For more information about using the Adprep, see Active Directory Help.

The version of the Active Directory schema of the source forest is not compatible with the version of Active Directory on this computer.
-----------------------------------------------------------------------

I dont have the CD's either, this OS came preinstalled.


Any ideas?

THANKS!!!
~Void

 

What operating system is the server running that is acting as the primary?