How to sync 2 Laptops to Lightroom?

I am trying to figure out what is the best way to sync my lightroom catalog between my 2 laptop / notebooks through a 120gb mini external HD?
I have searched and googled and everyone seems to recommend watchingMoving Between Laptop and Desktop by Matt Kloskowski, but I cannot find an active video anywhere.

ttt

Do you have all the images, previews, xmp files and the .lct file on the external?

Don't see why you shouldn't be able to open it on either machine.

I do this between two laptops.
It's really easy provided you have all the files that are in your catalog, located on the external hard drive.

You really just open up the catalog in the other LR.
All changes that will be made in the catalog on one computer, will open up in the same catalog on the other.

Hope this clarifies it for ya.

I have 15,000 pictures in my Catalog. 4,000 on my main Laptop and the rest on the external.
Basically I want to be able to take my small laptop with me to edit pictures on shoots or in studio and have everything sync up properly.

Well, you can keep shots in your catalog even if they aren't "online", but of course you won't be able to edit them when traveling. What you can do is copy your catalog folder onto your laptop when you are leaving and import photos into it then when you return you can copy it back onto your main computer, use the Lightroom utility to Find missing files and folders to locate new stuff, and use Lightroom to move folders from the laptop to the main computer.

That's just one of several possible approaches -- Lightroom is designed to make things doable in a few different ways.

Here's another thing you can do. You can "merge" catalogs" together. So if you go off site, edit the files on the laptop. Then you can export the images as a "catalog" on the laptop. When you get home, you can then import the catalog on the home computer's LR. This will bring in all the actual photos, edits, and catalog database stuff to the "home" computer with the big HD.