Install Lion/Mountain Lion on a New HDD/SDD
Be sure you backup your files to an external drive or second internal drive because the following procedure will remove everything from the hard drive.
Boot to the Your OS Recovery HD:
Restart the computer and after the chime press and hold down the COMMAND- R keys until the Recovery HD's main menu appears.
Partition and Format the hard drive:
1. Select Disk Utility from the main menu and click on the Continue button.
2. After DU loads select your new SSD (this is the entry with the mfgr.'s ID and size) from the left side list. Click on the Partition tab in the DU main window.
3. Under the Volume Scheme heading set the number of partitions from the drop down menu to one. Click on the Options button, set the partition scheme to GUID then click on the OK button. Set the format type to Mac OS Extended (Journaled.) Click on the Partition button and wait until the process has completed. Quit DU and return to the main menu.
Reinstall Lion/Mountain Lion: Select Reinstall Lion/Mountain Lion and click on the Install button. Be sure to select the SSD as the destination.
Note: You will need an active Internet connection. I suggest using Ethernet if possible because it is three times faster than wireless.
Now, boot from the SSD to assure it will boot the computer. Open Users & Groups preferences and click on the lock to authenticate. CTRL- or RIGHT-click on the account listed for the SSD and select Advanced Options from the context menu. You will note a field labeled Home Directory: with a button on the right labeled Choose. Click on the button. A file dialog will appear. Locate the Home folder on your HDD. Select the entry and click on the Open button. This will return you to the Advanced Options window. You must now Restart your computer.
After the restart you will be booting from the SSD but using the Home folder on the HDD from which you used to boot.