Can't get Itunes to work or install - Tried Everything

Question

OK! It started as Itunes would not load on one of my users on Win XP (although it did work on1).
I recently formatted my whole computer. I reinstalled Itunes and Quicktime using the current update from the apple website, and both worked fine on my user. However, on the 3 other users on the computer, neither work.
I have tried to uninstall Quicktime (on both my user and other users) and everytime get the error message :
"Error:- 1603 Fatal error during installation..."
I have even tried using windows install cleanup as mentioned earlier and then trying to reinstall quicktime from a stand alone update (however, this still does not work as I get the same error message as above).
I cannot edit the registry because every time I get a message saying:
"Cannot open Apple Computer Inc, Error while opening key"
I have tried system restore and then reinstalled iTunes but that doesnt work.
I have also tried the solution with the iTunes folder in My music.
BUT NOTHING IS WORKING
Now iTunes will not load on any user and I cannot install quicktime as it comes up saying :
"Quicktime failed to initialize" Error # 63441"
I have thoroughly searched the discussions and not found a solution.
I really am stuck, so if anyone has any suggestions, I would really really appreciate them!
Evesham 2.4ghz P4   Windows XP  

Answer 1

hi drummerman!
sorry for the delay in getting back to you.
my hypothesis at the moment is that you've actually got three different rare problems all piled on top of each other.
(1) a rare variation on the weird rare registry/user-account thing (in which itunes will open in one preexisting account but not in other preexisting user accounts). i've seen that new Error # 63441 (or similar error numbers) show up under those circumstances too.
(2) a really rare sort of registry-related 1603. (i think i've only seen that about three times in toto.)
(3) and to cap it off, that strange situation where the registry isn't allowing you to make any edits ... which would compromise the techniques i've seen used with some success against similar versions of 1 and 2.
... so we're going to be experimenting for a little while, trying to get some toeholds on the rock wall of progress.
the first experiment is going to be related to confirming my diagnosis in (1) and trying to get around (3).
head into your user accounts control panel, and try to create a new user account with full administrative privileges. (there's help documentation on that to the left of the control panel screen.) while you're in that control panel, switch off fast user switching in your logging-on preferences.
now log out of whichever old account you were in, and log in to the new account.
(1) does itunes launch successfully from inside the new account?
(2) does the registry allow you to make any edits from inside the new account?
keep us posted. (i'm moving a little slowly through reply backlogs and whatnot at the moment, but i will be back to check on your progress.)
love, b