I go crazy when I open Outlook links for pages with Flash animations and stuff and it opens in Internet Explorer 64 bit! These things simply don't appear, since there aren't still plugins for these things.
Rename C:\Program Files\Internet Explorer to C:\Program Files\Internet Explorer64bit
Copy C:\Program Files (x86)\Internet Explorer to C:\Program Files
I know, it's kind of tricky, but it gets the job done, and without losing the 64bit version.
Update: Change default .mht file program