Excerpted from www.tuaw.com
by TJ Luoma (with edits from Peter Miazga)
If you are using Leopard (10.5) or less, you must first upgrade to Snow Leopard.
Mac Outpost has this on order from Apple Canada and they will be available while supplies last for $34.99. Note: if you are running a version of Mac OS X before 10.5, you should buy the $149.99 Mac Box Set which includes Snow Leopard, iLife ’11 and iWork, but that is a legal/moral obligation, not a technical one. The Snow Leopard DVD will work on any supported Mac, regardless of which OS is installed on it (or even on a new drive). Mac Outpost does not advise that clients “skip” the box set in favor of the less expensive upgrade as it is not “legal” and could likely cause compatibility issues.
Not sure what version you are running? Go to the Apple menu and select “About This Mac” and look in the window that appears (see image above). If it says anything starting with 10.6, you are running Snow Leopard. Anything less? Time to upgrade.
(If you are running Snow Leopard, make sure you are running at least version 10.6.6 and get the Mac App Store app!)
You may also want to make sure your Mac is compatible. Apple specifies “[y]our Mac must have an Intel Core 2 Duo, Core i3, Core i5, Core i7, or Xeon processor to run Lion.” That information is shown in the “Processor” line of the “About Mac” window, shown above.
Please call the store or email us for more details!