Windows Installer error during iTune install in vista

a. Click Start, click Run, type regedit in the Open text box, and then click OK.
b. Expand HKEY_LOCAL_MACHINE, expand SYSTEM, expand CurrentControlSet, expand Services, and then click MSIServer.
c. In the right pane, right-click ImagePath, and then click Modify.
d. In the Value data text box, type the location of the Msiexec.exe file that you determined in step 1, followed by the value of /V , and then click OK.
For example, if the location of the Msiexec.exe file is C:\Windows\system32\Msiexec.exe , type the following text in the Value data text box:
C:\WINDOWS\System32\msiexec.exe /V

restart the computer in safe mode with networking
register the windows installer msiexec /regserver
restart the computer in normal mode
In your registry you will have a registry key called: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSIServer
Now for some reason your installation might have a value in this key called:WOW64 and it probably has value 0x00000001 (1)
Now THAT's the whole problem right there. This value tells Windows Installer only to deal with 32-bit installers and to return you an error whenever you try to install something that is 64-bit. To fix it, just set the value to 0. So you will see in your editor:
WOW64 REG_DWORD 0x00000000 (0)

restart the computer and tried to install iTunes