Upgrading itunes 10.7 to 11. Invalid Signature error

Hi,

I'm getting an error when trying to upgrade itunes & quicktime to the latest version. I get the error invalid signature and it stops. This happens for itunes, quicktime and the shared files.

I did try and download directly (rather than through itunes but got an error about itunes not being a 32 bit version which is strange because I'm using a 64 bit pc. So I found a 32 bit version however that returned a side by sid configuration error.

Any suggestions?