ITunes won’t install, please help me.

Hello.
I tried to update iTunes for my new iPhone 4.O and did it because my iPhone did not connect with older versions of it. It didn't update. I uninstalled it and tried to reinstall it but I get this error.
"error has occurred during installation assembly."
Then I pressed OK and it says "status: rolling back". It says that Apple Mobile Device wouldn't start too. I tried a lot of ways but all goes in vain. Went through the forums and everything but was unable to solve this.
I have uninstalled every application that iTunes comes with for a clean new installation but When I try to cancel the installation after all of these error messages and it just will NOT go away.
Finally I ended this task and tried to reinstall it but this time it says that my system isn't modified for iTunes and have to install later.
Please help me to fix this.
Thank you.
