Answer
This question was answered on June 20, 2007.
Much of the information contained herein may have changed since posting.
I am using Outlook 2007 as well and have had issues with slow downs on opening emails. I suggest downloading the Outlook Performance update from Microsoft's website. As it so happens, i have the link for the update. http://www.microsoft.com/downloads/details.aspx?FamilyId=C262BCFD-1E09-49B6-9003-C4C47539DF66&displaylang=en
There are steps that you can do manually if this doesn't fix the issue.
My first solution would be to rename or delete outcmd.dat, extend.dat, views.dat and frmcache.dat. Outlook will recreate these files as needed.
Look for these files at:
Outcmd.dat:
C:\Documents and Settings\<username>\Local Settings\Application Data\Microsoft\Outlook (Windows XP)
C:\Users\<username>\AppData\Roaming\Microsoft\Outlook (Vista)
Extend.dat:
C:\Documents and Settings\<username>\Application Data\Microsoft\Outlook (Windows XP)
C:\Users\<username>\AppData\Local\Microsoft\Outlook (Vista)
Frmcache.dat:
C:\Documents and Settings\<username>\Application Data\Microsoft\Outlook (Windows XP)
C:\Users\<username>\AppData\Local\Microsoft\FORMS (Vista)
Views.dat:
I hope this helps as this method has helped me.
>http://www.computerhaven.info/forum/tm.aspx?m=54163</p>