You need to keep your versions straight or you will get the wrong advice. You need OSX version 10.6.8 (or higher) to use iTunes version 10.7.
1) Make sure your computer meets Snow Leopard technical specifications - http://support.apple.com/kb/SP575 This mostly means making sure it is an Intel Mac (a MacBook is) and has at least 1GB RAM (more is recommended). To check RAM, go to the Apple in the upper left corner of any window, then "About This Mac". Now continue to "More Info...". It should say you have at least 1GB of "memory".
2) Apple no longer carries 10.6 in its stores or online. Telephone Apple to purchase a Snow Leopard disc. In the USA: (800) 676-2775 (contact information for other countries: http://support.apple.com/kb/HE57)
Alternatively you can buy from online retailers but anticipate paying much more than the original price which is the price still charged by Apple
3) Backing up your computer before upgrading is always a good idea.
4) After installing from the DVD, update your Snow Leopard installation using Software Update or manually downloading and installing the Mac OS X 10.6.8 Update Combo v.1.1 - http://support.apple.com/kb/DL1399
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iTunes 10.7 needs Mac OS X 10.6.8. See if your computer is supported > http://support.apple.com/kb/sp575 Call Apple to buy Snow Leopard > http://support.apple.com/kb/HE57 Then, make a backup, insert the DVD and upgrade. Finally, open > Software Update and install the latest version