Purchase Mac OS X 10.6 on DVD(or get it for free if you're a paid MobileMe member), update it to at least 10.6.6, and then get Lion from the Mac App Store, or purchase Mac OS X 10.7 on the USB thumbdrive.
Your profile shows you are running Mac OS X 10.5.8. iCloud requires version 10.7.2. Go to the Apple menu in the upper left > About this Mac > More Info. Post your system specs here and we can tell you if you can upgrade to Lion. Please do not include the serial number or UUID.