Making Leopard bootable on ext. drive

I see there is an article here http://www.macfixit.com/article.php?story=20071025100548752

And I really want the installer to be on it's own partition as well as a freshly installed version of Leopard.

The article speaks about one single DVD but the Leopard that came with my machine and I guess every copy of Leopard is two DVDs? How should I handle this case as it is unclear from the article. Thanks in advance.

 

Even though I'm still confused by the one disk (not two) thing, I decided to proceed.

But following the above link the instructions are:

<quote>Now we're going to copy the image to the FireWire drive. You'll see that it is listed in the left-hand column of Disk Utility. Select it and press Open. The disk image is now mounted. Again, you'll see it listed in the left-hand column as two volumes, arranged hierarchically. What you want to clone is the inner (lower) volume, called "Mac OS X Install DVD". Switch to the Restore pane. You'll see two fields: Source and Destination. Drag the listing for "Mac OS X Install DVD" from the left-hand column into Source. Drag the listing for the small partition on your external FireWire drive from the left-hand column into Destination. Check both checkboxes (Erase Destination and Skip Checksum) and press Restore. Wait until the image has been copied to the FireDrive drive. You will now have two "Mac OS X Install DVD" listings in the left-hand column: one is on your FireWire drive (in the upper area of the listings), the other belongs to the disk image file (in the lower area of the listings). You can now unmount the one belonging to the disk image file.</quote>

If I mount the image I can not drag it to be source (and if I manually go to select the .cdr file it is greyed out). I can select it if unmounted (the "outer volume"). Any ideas?

 

So if I was to install a retail copy on my machine what difference would I notice to the two disc version?