According to Apple, this error may occur without a corresponding error message when you install iTunes 5 or later on a system with Windows XP Service Pack 2. This error is caused by either a conflict with antivirus software or with improper user-privilege configurations in Windows. 

 Solution:
 Apple says you should take the following steps to resolve this problem.
 
 First try disabling your antivirus software. Then attempt to install iTunes again. After you install iTunes, you can re-enable your antivirus software.
 
 If disabling your antivirus software didn't fix the problem, you should check the user privileges on your computer.
 
 If you have WinXP Home installed on your system, you will need to perform an installation repair of Windows. First, back up any important files in case of a Windows repair failure. Then insert the WinXP Home installation or upgrade disc in the drive. If you are prompted to restart your computer, do so. If not, click Start and Shut Down. Select Restart from the drop-down menu and click OK.
 
 After your system restarts from the installation disc, choose the option to install Windows. Next, the installation disc will prompt you to either perform a new installation or to repair an existing installation. You want to choose the repair option. The computer will reboot automatically when the repair is complete. After your computer restarts, you should be able to re-install iTunes.
 
 If you have WinXP Pro installed on your system, the procedures are different. First, click the Start menu, Settings, and Control Panel. Double-click Administrative Tools and Local Security Policy. In the left pane, under Security Settings, double-click Local Policies. Then, in the right pane, double-click User Rights Assignment. A list of policies appears in the right pane. Double-click Impersonate A Client After Authentication. In the resulting dialog box, both Administrators and Service should be listed. If either Administrators or Service are missing from the list, click the Add User Or Group button. Then click the Object Types button. Make sure that both the Users and Groups checkboxes are selected. Then click OK. In the Enter The Object Names To Select field, type SERVICE;Administrators. Click the Check Names button. The text you typed should be underlined. You may see the name of your computer in front of Administrators. Click the OK button. Click OK one more time. Then restart your computer and re-install iTunes.