Downgrade Exchange 2007 B2 to Exchange 2003 SP2

Oh, what fun and games I had.

First I backed up all the mail:

• Outlook export to PST
• ExMerge (Hey - It worked on Exchange 2007!)
• NT Backup of store

Then I removed Exchange 2007 and reininstalled Exchange 2003 - Except it didn't quite go that smooth,

The installation errored saying that it could not install the information store and to check the install log. I found this error message:
mode = 'Install' (61953) CBaseAtom::ScSetup (f:\titanium\admin\src\udog\setupbase\basecomp\baseatom.cxx:842)
Error code 0XC00736B1 (14001): This application has failed to start because the application configuration is incorrect. Reinstalling the application may fix this problem.

Tracing back up the install log found this message:
Interpreting line -- ID:31259 --
CInsParser::ScProcessLine (f:\titanium\admin\src\libs\exsetup\hiddenw1.cxx:1225)
Error code 0XC00736B1 (14001): This application has failed to start because the application configuration is incorrect. Reinstalling the application may fix this problem.

Tracing back futher led to this line:
Copying c:\program files\common files\microsoft shared\cdo\cdoex.dll
Preserving existing copy of c:\program files\common files\microsoft shared\cdo\cdoex.dll
Sure enough, typing "regsvr32 c:\program files\common files\microsoft shared\cdo\cdoex.dll" produced the same error code.

I deleted the copy of cdoex.dll and replaced it with the copy from the Exchange Server 2003 CD and re-ran the regsvr32 command - It worked. I clicked "Retry" and the install completed.

I did receive an error message about the wrong version of mapi32.dll being on the hard disk so I also replaced from the CD too.

Applied Exchange 2003 SP2 and visited Microsoft update to apply some hot fixes and everything appears to be working well.