downloading issues

Hi peeps,

i dont know if i am in the right category but here goes.

I am having troubles downloading iTunes and any updates for my Macbook Pro. I use my iPhone connected by usb for my internet, and i can download the updates, but when it goes to install, is says it's either corrupt or unable to install. I cant download my iphone software either because it comes up with an error.

what do i do??

thanks
Nyssa

itunes says the disk is unverified, whether i DL it through itunes or the website.....
***?