If you choose an Upgrade installation, then the Office 2007 setup
program will replace your Office 2000 applications with the
corresponding Office 2007 applications. If you have an Office 2000
application that does not have a corresponding Office 2007 application,
then that Office 2000 application will remain on your computer.
If you choose a Custom installation, then in the Installation Options
tab you can choose to keep your old Office 2000 applications alongside
your new Office 2007 applications. But you can only have one version of
Outlook on your computer, so you need to decide whether you want Outlook
2000 or Outlook 2007.
Just in case Something Bad happens, you should back up your Word
normal.dot template and other customized files as described at
http://word.mvps.org/FAQs/General/FilesToBackup.htm before you install
Office 2007.
