You should delete the FirstRun registry value.

 Code:
$rc = DelValue("HKCU\Software\Microsoft\Office\11.0\Outlook\Setup", "First-Run")


The 11.0 part should be changed to fit your needs.

9.0 = Office/Outlook 2000 (could also be 09.0 not sure. I do not have Office2K anymore)
10.0 = Office/Outlook XP (2002)
11.0 = Office/Outlook 2003
12.0 = Office/Outlook 2007

[edit]
Using Glenn's code below might be best to get the office/outlook version when you have several versions installed.
[/edit]

Edited by Mart (2009-03-10 05:47 PM)
Edit Reason: Added a comment.
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Mart

- Chuck Norris once sold ebay to ebay on ebay.