Auch, I manage it!
I've been trying by trial and error since yesterday.
After a thorough clean up from all references to iTunes and QuickTime I tried installing QT 7.0.3 stand alone as someone suggested, but it didn't work.
Anyway, I have eventually found an old Quicktime/iTunes installation dating back to September. I think it was in C:\windows\installer, but I can't find it anymore now, so I might be wrong.
I ran QT installer that was there (7.0.2) - OK
Then iTunes 5-something - OK
Now i had an old iTunes in need OS a security update...
Worked with it for a short while - OK - Nice.
Out and in again in windows xp.
Installed on top of the old files the last iTunes setup. It complained again about the -3 error while installing QT 7.0.3, but after that it said it was all well.
In fact I have my iTunes alive and kinkin' - at last!