Sorry about the delay aid8me. I've been dwelling on how best to proceed next.
I think we'll try first treating this as if it we were treating a more-standard sort of Apple Application Support installation error where we suspect security software interference on the install. If no joy with that, we'll work up to a more aggressive set of treatments.
Best to print out a copy of these instructions, because at one point of proceeding you won't be able to use a web browser.
Preliminaries
Download and save a fresh iTunes installer to your hard drive. (Don't run the install on line and don't start the iTunes install just yet.)
http://www.apple.com/itunes/download/
Now, quit QuickTime (if you have that open) and Safari 4.0.4 (if you have that installed and open). Both applications use Apple Application Support, and they will interfere with the uninstall if you have them open.
*Uninstall phase*
Head into your "Uninstall a Program" control panel. Uninstall iTunes. Uninstall Apple Application Support.
(From this point on until we reinstall Apple Application Support, neither QuickTime nor Safari 4.0.4 will be able to run.)
Next we'll remove any leftover program files and folders.
(1) Open "Local Disk (C:)" or whichever drive your program files are stored on.
(2) Open the "Program Files" folder.
(3) Right-click on the iTunes folder (if it still exists) and select "Delete".
(4) Go back to "Local Disk (C:)" or whichever drive your program files are stored on.
(5) Open the "Program Files (x86)" folder
(6) Right-click on the iTunes folder (if it still exists) and select "Delete".
(7) Staying in *Program Files x86,* open the "Common files" folder.
(8) Open the "Apple" folder.
(9) Right-click on the Apple Application Support folder (if it still exists) and select "Delete".
Now empty your Recycle Bin and restart the PC.
*Reinstall Phase*
After the PC restarts, *do not* open any other applications. Disconnect from your network and/or the internet. Switch off
all your security software (firewall, antivirus and antispyware).
Now start the install by doubleclicking the iTunes64Setup.exe file you downloaded earlier.
Reenable all security software prior to reconnecting to your network and/or the internet.
Did the install seem to go through okay? Or do we still get the same sort of 1935 error on the Apple Application Support part of the install?