Here are my notes on that (I'm running Vista 64 Ultimate):

RUNNING MULTIPLE INSTANCES OF OUTLOOK

Download and install "ExtraOutlook.exe" from:

http://www.hammerofgod.com/download/ExtraOutlook.zip

Copy the executable to the folder where outlook lives. In the current case that means:

  C:\Program Files (x86)\Microsoft Office\Office12\

Create a profile for each separate instance of Outlook we want to run:

To create and manage profiles in Vista 64 go to

  Control Panel > View 32-bit Control Panel Items > Mail > Show Profiles

Create or modify the Outlook shortcut on the desktop to access the desired profile:

Profile 1:

  "C:\Program Files (x86)\Microsoft Office\Office12\ExtraOutlook.exe" "C:\Program Files (x86)\Microsoft Office\Office12\OUTLOOK.EXE" /profile "Profile 1"

Make a duplicate copy and then...

Profile 2:

  "C:\Program Files (x86)\Microsoft Office\Office12\ExtraOutlook.exe" "C:\Program Files (x86)\Microsoft Office\Office12\OUTLOOK.EXE" /profile "Profile 2"

Now two instances of Outlook can be opened and each is independently accessing the corresponding profile's data.

I go through the extra effort of assigning a different icon to each account and placing them on the quick-launch toolbar. I've been doing this for about two years and it works great. No issues whatsoever.

I can't believe MS doesn't implement MDI in Outlook so that one can do this using tabs and a single instance.