Not sure, but this may help someone having problems installing SP1.
After several failed attempts to install SP1 (followed many ideas in forum) I finally saw a post here that said that if you cannot get a clean run of SFC you will never be able to install SP1.
Well I could not get a clean SFC after several runs, so bit the bullet and did a clean install, installed all updates including SP1. Ya Hoo.
Ran SFC after each program reload - all clean. I then reinstalled the Windows Mail hack and got it all running fine. The next SFC failed. Oops.
Checked the CBS log and sure enough it could not repair the hacked version of MSOE.dll.
I temporarily installed the original msoe.dll back into the WindowsMail directory and re-ran SFC. Still fails with same errors.??? Perhaps the hacked registry changes are getting in the way.
Oh well. I like Windows Mail so itís staying. If another SP comes along, I will just revert back to an Image of Pre-Windows Mail install then do updates.