How do I upgrade my OS X v5.8 to v6?

If you're using a PowerPC Mac, you can't.

If you're using an Intel Mac, phone the Apple Store and order it.

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If you need to purchase Snow Leopard you can still purchase a copy from Apple's online store's telesales agents.[1-800-MY-APPLE (1-800-692-7753) or Customer Service and Sales Support at 1-800-676-2775.] Ask for a Sales Representative.

Third-party sources for Snow Leopard are:

Snow Leopard from Amazon.com

Snow Leopard from eBay

After you install Snow Leopard you will have to download and install the Mac OS X 10.6.8 Update Combo v1.1 to update Snow Leopard to 10.6.8 and give you access to the App Store.