I know the Zune theme has been around for a while and may be old news to most of you but there is a simple solution to the error that is output when a user tries to install the ZuneDesktopTheme.msi from Microsoft on a x64 version of Windows.
1. Search Google for a file called orca.msi, this is a MSI "manipulation" tool from MS.
1a. Or you can download it from here
2. Install orca, the defaults are fine
3. Download the Zune desktop theme, the direct link from MS is above ^
4. Right click on the ZuneDesktopTheme.msi and select edit with Orca
5. Under the Tables section(left) go to InstallExecuteSequence
6. In the Action-Condition-Sequence section(right) highlight LaunchConditions and Del
6A. Or right click the LaunchCondtions entry in the database and select Drop row
7. Answer yes to the prompt and then save and exit
8. Install the MSI as normal