Hi Martin
A few Microsoft Knowledge Base articles exist for this sort of error (though for previous Office versions). Have a quick look, and see if the fixes might apply to your Office 2007 errors.
http://support.microsoft.com/kb/296056/en-us
http://support.microsoft.com/kb/324852/en-us
All the indications point to permissions trouble: if it's the ".msi" files mentioned in your post, you can try right-clicking them, checking their "Properties", and seeing if they are set to "read only" (if so, remove the checkmark from "read only").
Best of luck
. . . Gary