How do I setup an external start up drive

Hello, first you need to Format it likely...

How to format your disks...

http://www.kenstone.net/fcp_homepage/partitioning_tiger.html

(To Install OSX on an IntelMac the Drive it needs the GUID Partitioning scheme mentioned at the bottom.)

Thanks to Pondini, Formatting, Partitioning, Verifying, and Repairing Disks...

http://Pondini.org/OSX/DU.html

Then you can clone your internal drive to it, or Install OSX to it.

You can also hold the Option or alt key at bootup to select your boot drive.

Drive Preparation

1. Open Disk Utility in your Utilities folder. Have the external drive connected.

2. After DU loads select your hard drive (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.

4. Select the volume you just created (this is the sub-entry under the drive entry) from the left side list. Click on the Erase tab in the DU main window.

5. Set the format type to Mac OS Extended (Journaled.) Click on the Security button, check the button for Zero Data and click on OK to return to the Erase window.

6. Click on the Erase button. The format process can take up to several hours depending upon the drive size.

At this point you have two options. You may clone your existing startup drive to the external drive or you can do a clean install of Lion on the external drive.

Clone Lion using Restore Option of Disk Utility

Boot to the Recovery HD:

Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.

1. Select Disk Utility from the main menu then press the Continue button.
2. Select the destination volume from the left side list.
3. Click on the Restore tab in the DU main window.
4. Check the box labeled Erase destination.
5. Select the destination volume from the left side list and drag it to the Destination entry field.
6. Select the source volume from the left side list and drag it to the Source entry field.
7. Double-check you got it right, then click on the Restore button.

Destination means the external drive. Source means the internal startup drive.

Install Lion from Scratch

Boot to the Recovery HD:

Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.

Install Lion: Select Reinstall Lion and click on the Install button. Be sure to set the external drive as the target before you click on the Install button.