Permalinking problem WP2.6 on Windows IIS

Ok, here’s the deal:
I’m running my dad’s website for his business with WP 2.6 as a CMS. Now he is with this hosting company which only provides Windows IIS servers. Permalinks used to never work, but since 2.6 I was suddenly able to do run with nice permalinks! Yay! But lately I found out it only had 404’s again. I tried some htppd.ini or whatever fixes provided by my dad’s host, but this one doesn’t work for me.. Maybe because it doesn’t work since 2.6 anymore. I don’t know!
So, how can you make use of nice permalinks on a Windows IIS server with WP 2.6?