Here is a list of the extensions you might want to add to the host settings so that you can upload Office 2007 documents.

docm,docx,dotm,dotx,potm,potx,ppam,ppsm,ppsx,pptm,pptx,xlam,xlsb,xlsm,xlsx,xltm,xltx

This will allow you to upload files in the Office 2007 format and if you use the documents module you will be able to download them.

Of course there is a catch. IIS, Microsoft's web server isn't  ready to handle these extensions either.  So, if you want to create a direct link to the file and not use the documents module you have 2 choices:

1. Zip the file and post it that way.
2. Change the Mime Types for IIS

Option 1 is pretty straightforward.  Option 2 requires access to the server and some work:

For option 2 you can look at my blog: Office 2007 and DotNetNuke.