Did you previously have an E: drive (probably a CD) which has changed and no
longer available? Is there a CD in the drive if it is available?
I've only seen this (not with Office but could as well have been) when I added
another drive and letters got changed.
You can simulate a "drive E:" by mapping a network drive, even if it's to your
own computer.
All I can think of really. A little more detail might help, like is this a new
CD you've never used before? Are you trying to re-install something or install
an additional Office feature? If so, then I imagine it was installed from
drive E: (and must be in future, unless totally uninstalled)
Chris