When you ran Quicktime Preferences from the control panel and got that message about Rundll32, did you give the error message *in full*? Usually there is more, there is an important bit that is missing.
Anyway it seems you have a Quicktime problem which has to be fixed before worrying about iTunes.
One cause of Quicktime problems is the installation of an incompatible codec pack.
Have you installed any of the following:
ACE & K-Lite mega codecs package, QT alternative, Storm codec, WinAVI video converter
If so you need to uninstall them.
Then/otherwise try a full removal of QUicktime and reinstall.
Download the stand alone version of Quicktime (the one without iTunes)
http://www.apple.com/quicktime/download/win.htm
Remove Quicktime using the method in the following article (just Quicktime).
http://support.apple.com/kb/HT1923
The most important bit is the removal of the QUicktime files from the System32 folder.
Restart your PC
The install the stand alone Quicktime.
If that goes OK check to see if iTunes works.