iTunes 10.6 will not install, says a newer version exists.. i have 10.3

I have Windows Vista and iTunes has always installed quickly and easily

i just bought an iPad3 and i need to update the iTunes software 10.3.1.55 and i am trying to install the newest version 10.6.3.25 x64 and it goes through the whole install process and says "A later version of apple software update is already installed on this computer"

How can i go about force installing 10.6.3.25...

Thank you for any help in advancew