AVIVO has been rebranded, so it's now called "AMD Media Codec Pack
1) Download it
2) Run it to extract the contents. Pay attention to where they go (C:\ATI\Support\11-10_vista_win7_32-64_xcode\Packages\Apps)
3) Cancel the installer if you're not using an AMD GPU
4) Navigate to the location noted in #2 and select the correct version
of AVIVO for your platform, open the directory, and run the installer
5) Don't panic when you see this error message:
6) Open an elevated cmd prompt and navigate to "C:\Program Files\Common Files\ATI Technologies\Multimedia"
7) regsvr32 the appropriate atimpenc dll for your platform
8) If the regsvr32 files, you probably don't have the necessary Visual
Studio runtime installed. It looks like these are also in the folder
from #2, but I'd go grab the latest VS2010 rev from MS.