I want to upgrade the hard drive in my Mac Pro 1,1 2006 2x2.66GHz Xeon
Acquiring Snow Leopard 10.6

Should you need the physical disk, you can order the Snow Leopard 10.6 installation disk directly from Apple, from this page: http://www.apple.com/shop/product/MC573Z/A/mac-os-x-106-snow-leopard

Acquiring Lion 10.7

Likewise, you can order Lion 10.7 from Apple, from this page: http://www.apple.com/shop/product/D6106Z/A/os-x-lion.  Note that you will not receive physical disks, but an email with a content code for the Mac App Store that you can use to download the Lion 10.7 upgrade.

If you had not already purchased Lion 10.7 through the App Store (before July 2012), you will no longer be able to locate it there; Apple has removed it and Lion 10.7 can no longer be purchased for download through the App Store.  As you're using 2006-era hardware, you will not be able to upgrade to a newer OS version than Lion 10.7.  See this MacWorld article for additional information.

Upgrading the Hard Drive

This fantastic article shows how to replace the hard drive on a Mac Pro machine.  Follow the steps, and you will have the new hard drive functional in just a few minutes.

The basic steps are:


Make sure that you have a compatible SSD (check the compatibility chart for the SSD vendor)
Get your small Phillips head screwdriver ready in advance
Follow proper anti-static procedures (static kills computer equipment)
Open and remove the side access door, using the latch on the rear of the machine
Choose an empty hard drive bay, make sure that it's unlocked, and pull it out
Connect the SSD to the tray using the 4 Phillips head screws
Slide the tray (with SSD) back into place in the machine and make sure that it is properly seated
Replace and close the side access door


At this point, you will have the original hard drive and the new SSD installed and ready for use.

Transfer Content to New Hard Drive

You can use the Disk Utility program to transfer the content from your previous Snow Leopard hard disk to the new SSD.  Detailed instructions can be found in this article.

The essential steps are:


Boot into Recovery Mode (hold ⌘ R during boot)
Launch Disk Utility from Recovery Mode
Select the disk partition
Choose the Restore pane on the right side of the window
Select the target partition (the new SSD)
Click the Restore button to start the cloning process


Be prepared for the process to take a considerable amount of time, especially if the original hard disk has a lot of content; all of that content needs to be moved.

Upgrading to Lion 10.7

This is a great point to do the upgrade to Lion 10.7, because you now have a backup copy of the original hard drive and can safely restore if any problems occur.

LifeHacker has a great article that covers the upgrade process.

These steps can be summarized as such:


Check your machine's compatibility against the specs
Update your OS X system and apps before you start
Open the App Store, go to Purchases, and enter your Lion 10.7 content code
If you cannot see the Lion download at this point, hold the ⌘ key and click the Purchases tab again and click Download
After the download is complete, click the Continue button on the installation window
Agree to the license terms, choose your SSD volume, and provide your Administrator password when prompted
The installation process will begin, and may take some time as your system is upgraded
Once installation has completed, restart your machine
Update your OS X system and apps to the current compatible versions


At this point, you should have a fully functional Lion 10.7 installation, ready for use.

Cleaning Up

Once the SSD has all of the content from the original hard drive, the hard drive may either be removed or used as a secondary storage location.  Remember that this is a 12-year-old hard drive, and operational lifetimes for hard drives are typically in the 5-8 year range.  If there are any issues at all with the hard drive, you're better off removing and disposing of it (many electronics stores will properly dispose of it for you).

If you decide to keep the original hard disk, this can give you quite a lot of available disk space, but you should erase or repartition it for 2 main reasons:


to prevent boot-time confusion about which volume (disk) is primary
to reclaim the storage used by the content that is now cloned to the SSD