» A Mac computer running OS X 10.5.8 or newer with a USB 2.0 port, or a Windows computer with a USB 2.0 port and Windows 7, Vista, or XP Home or Professional with Service Pack 3 or newer. Note that the system requirements are constantly changing as both iPhone and computer features evolve. We recommend viewing the most recent system requirements before you make any purchase decision (http://www.apple.com/iphone/specs.html).
» iTunes 9.2 or newer.
» iTunes Store account.
» Internet access.
Before you purchase an iPhone, make sure that you have a computer on hand that is up to the task.
NOTE: If you haven’t installed iTunes on your computer, download a free copy from http://www.apple.com/itunes. Versions are available for both Mac OS X and Windows systems, and they’re easy and quick to install.
Source of Information : Taking Your iPhone 4 to the Max