At this time (version 2 Beta 1), in the life of Silverlight there is no 64-bit support. I'm not certain if or when 64-bit support will appear, but I don't think Vista 64-bit users should go without Silverlight. And the good news is they don't have to.
In most cases, running Silverlight applications should not be an issue. IE7 and Firefox run in 32-bit mode by default allowing Silverlight to run as expected.
A different scenario which needs some attention is Sidebar Gadgets that use Silverlight. The Windows Sidebar application (sidebar.exe) runs by default in 64-bit mode and in order to use a Silverlight-based gadget you need to run sidebar.exe in 32-bit mode.
You can do this simply by closing the default Sidebar and navigating to C:\Program Files (x86)\Windows Sidebar and double-clicking sidebar.exe. Now you can successfully run the new Channel 9 gadget or Xbox Friends Watch in your sidebar and enjoy knowing what the latest C9 video or or when your Xbox friends are online.
If you're happy with the results, you can make sure the 32-bit version of Sidebar is added to your system startup by following the step below:
- If you are still running the 64-bit Sidebar, right-click the Sidebar and select Properties.
- Uncheck the Start Sidebar when Windows starts option and hit OK
- Open C:\Program Files (x86)\Windows Sidebar in Windows Explorer
- Right-click sidebar.exe and select Copy
- Right-click the Windows Orb and select Explore
- In Windows Explorer navigate to the folder entitled ..Programs/Startup
- Right-click in the folder and select Paste Shortcut