This has specific instructions for custom install:
http://office.microsoft.com/en-us/he...340671033.aspx

"Mary" wrote:

You must select Custom Install to deselect individual programs. Uncheck
everything but Outlook. Outlook 2007 will uninstall Outlook 2003. You can't
have 2 versions of OL. You might want to consider waiting since OL 2007 will
not integrate with the 2003 version. If you want to stop autoplay, hold the
Shift key down when you insert the Office disk.

"rusty" wrote:

I recently purchased Microsoft Office 2007 Small Business Edition. At this
time I only want to install Outlook. I want to wait till a project is
finished before I install the other programs. However, I don't see a custom
install. As soon as I put the DVD in the drive, it installs the whole works.
Any advice as to how to install selectively?