Where to begin... Outlook does have a speed problem, especially with html mail. And I'm using v.12 on Vista Ultimate.
  1. Try searching the MS newsgroups.
  2. The AV scan is a known issue with email. Disable it temporarily and see what happens.
  3. I've noticed, with IE7, that composing an email generated by a mailto: link takes forEVER.
  4. Google this: site:microsoft.com Outlook+slow+to+launch.
  5. Try the Outlook MVPS site.