Check Incredimail support to see what formats you can transfer/export to -
or google.

What, you finally grew tired of the childish interface?  The reliance on
HTML to bloat your mails, or how much time you waste creating a cutsy mail
only to have your recipients force reading in plain-text to wipe out all
that fluff crap?

From prior posts from Incredimail users, and from the replies to them, no,
Incredimail wants to keep you using their product by not providing any
export or format that Outlook or any other e-mail client would understand.
You got stuck royal where the sun don't shine when you went to Incredimail.
You could forward all your e-mails using Incredimail and then receive them
using Outlook.

Heard of Google?  Searching on "+incredimail +outlook" works, like finding
http://email.about.com/cs/incredimailtips/qt/et012403.htm.