Are you downloading the 32-bit version of iTunes? Here is the (corrected) link:
Scroll down and click the link that says "Get iTunes for Windows"
Message was edited by: arscheller
My apologies for the incorrect link in my first response; I added further instructions to ensure that you are selecting the Windows version as well.
When you say you downloaded it, are you saving it to your hard drive first and then installing it or are you trying to run it directly from an Apple server? You should save it to your hard drive first and then double click the installer once it has completely downloaded. Let me know if this still didn't solve the problem.
These ones are typically caused by underlying problems on the PC that also often cause Windows Updates to fail to install. If we can fix the Windows Update trouble, we can usually get the iTunes trouble cleaned up en passant.
Go into your Windows update and try to check for new updates. Do they fail to install? If so, go into your Update History and doubleclick the failures. What alphanumeric codes appear for you? Are they also 0x80070002s, or a different error code? If they're different, what codes are you getting in Windows Update?
Today, April 19, 2011
Okay ... not likely to be a Windows Update issue that has just recently come on, then.
The 80070002 errors acn be associated with damaged files or missing permissions, and conceivably software interference too. So let's throw a bunch of basic principles troubleshooting procedures along those lines at the problem.
First, I'd try running a disk check (chkdsk) over your C drive, or whichever drive you install your program files on.
There's Vista instructions in the following document.
Select both Automatically fix file system errors and Scan for and attempt recovery of bad sectors. You'll probably need to schedule the scan to run on restart. The disk check should take quite a while to run (if you're running it on the C). If it quits after a few minutes or seconds, something's interfering with the scan.
After that completes, download a fresh copy of iTunesSetup.exe from the Apple Website and save it to your hard drive. (Don't run the install on line, and don't start the install just yet.)
Restart the PC. After the PC restarts, do not open any applications. Disconnect from the internet and/or your network. Now disable all your security software (firewall, antivirus, antispyware).
Now start the iTunes install by right-clicking the iTunesSetup.exe and selecting "Run as administrator".
(Reenable all security software prior to reconnecting to the internet and/or your network.)
Any better luck with the install that time?