Rebuild the message store of Windows Mail / Rebuild the Windows Mail folder

In researching a problem that I had with Windows Mail on Vista(pre-sp1), I
ran into a couple of terms
These terms were in the 'workarounds' for KB941090

Rebuild the message store of Windows Mail

Rebuild the Windows Mail folder

Could someone give me a couple explanations?

Are either of these action 'destructive' to messages in INBOX or other
folders?

Thank you!!

 

The best step-by-step procedure I've seen for this is here:
http://www.vistax64.com/tutorials/62560-windows-mail-problems.html
Scroll down to the section labeled "PROBLEM TWO".

Note: Be forewarned that this is a laborious and error-prone
procedure. You would be better off leaving your buggy Windows Mail
and upgrading to Windows Live Mail:

http://get.live.com/wlmail/overview
The installer will seamlessly and automatically import all of your
WM accounts, settings, and emails.