Hi Kevin,
All thats needed to add new file types is to create icons in the correct naming in the /Data/SiteImages/Icons folder. So we can make a copy of the doc.gif and name it docx.gif and the xls.gif can be copied and named as xlsx.gif and so on. I will add those in my copy today so it will be in the next release but you can do the same on your installation.
Best,
Joe