I managed to get Myst V working in the Windows 7 beta.
When installing, set the install path to C:\Program Files\ (The 64-bit version will want to put it in C:\Program Files (x86)\)
I also normally delete the default path, so that it's just C:\Program Files\Myst V End of Ages... but for the sake of keeping this functional, leave it at default this time I left it at default (C:\Program Files\Ubisoft\Cyan Worlds\Myst V End Of Ages).
You also need to apply the patch found on the Myst Online: Uru Live forums and on the Ubisoft forums that fixes the "init" folder found in C:\Users\%username%\AppData\Local\Myst V End of Ages
After that, it ran perfectly for me.