Vista

The iTunes/QuickTime installer will fail with a "VBScript not installed" error on some installations of Vista. I'm not sure exactly what leads to this situation as it does not seem to affect all Vista users, but there is a relatively simple fix:

• Click Start, All Programs, Accessories then right click on Command Prompt and select "Run as Administrator"
• cd to your windows\system32 directory
• enter the following command:
  

  regsvr32 vbscript.dll

This will re-register VBScript and allow the iTunes installer to run.