For those of you who have tried to install iTunes on Vista many of you will be aware of the awful "error code 2738", which a quick browse over the Internet point out that VBScript is disabled by default in Vista.  An effort from Microsoft to shut down functionality that is commonly abused by virus writers.

This being a smart move towards a more secure operating system you thing large vendors such as Apple and Adobe (apparently Photoshop CS3 has a similar issue), would be falling into line with it.

Apple have acknowledged the bug and give the following workaround here;

Windows Vista

1. On the Start menu, click All Programs.
2. Click Accessories.
3. Right-click Command Prompt and choose Run as administrator from the shortcut menu.
4. When the User Account Control dialog appears, click Continue.
5. At the command prompt type the following:
   regsvr32 vbscript.dll
6. Press Enter on your keyboard.
7. A message should appear stating "DllRegisterServer in vbscript.dll succeeded."
8. Click OK and try installing iTunes or QuickTime again.

Yes their solution really is to open that security hole Microsoft decided to shut down.

CoderJournal does a much better job of describing this as he also explains how to shut it back down.  His guidance is specifically for those 64bit users out there, find it here, but it easily translates to 32bit as well.  The main difference being 64 bit users need to register VBScript from the SysWOW64 directory and not the usual system32.

Oh, and if you run regsvr32 /u vbscript.dll when you are finished your OS is returned back to the state it should be in!