Exchange Server 2003 problems

I am installing Exchange Server 2003 on a Windows 2003 server. I cannot get past the forestprep section as it keeps coming up with an error. I have spent days on Google and Microsoft sites with no success.

The error is:
Microsoft Exchange Installation Wizard Setup failed while installing sub-component Microsoft Windows Active Directory schema update with error code 0xC103798A (please consult the installation logs for a detailed description). You may cancel the installation or try the failed setup again.

Any ideas anyone?