Watch this video for instructions (it's done on a PC, but the process/idea is the same for Macs)... Watchwww.youtube.com

Good video but pc folders are different then macs so i had trouble backing up based on the video...I wanna back up my files on the external but i still want to keep my internal SSL folder. I use my mac 90% of the time but in some cases so i don't have to switch at the club i'd like to use the external.

Well, the process is the same, just the folder names are slightly different.

1) Copy the ScratchLIVE folder in the "Music" folder on the Mac's internal drive, paste it on the root level of the external drive, and rename it _ScratchLIVE_

2) Copy all the files from the internal drive to the external drive, keeping the same folder path for all the songs. So, I assume you also have your mp3s music files also in the "Music" folder, or in another folder in the Music folder, correct?

So example, say you have a folder called "Hiphop" in the "Music" folder, then the path is

/Users/<yourname>/Music/Hiphop/songs.mp3

(where <yourname> is whatever your user account name is on the Mac)

then on the external drive, make a new folder on the root level of the drive named "Users", go in that folder and make another new folder named "<yourname>", go into that folder and make a new folder named "Music", then go into this folder and finally copy the "Hiphop" folder from the "Music" folder on the internal drive and paste it into the "Music" folder on the external drive.

You can do it the way Konix suggests but I think this way might be a bit easier for most users:

There are a few things you need to do when moving a library.

First is to download the latest version of SSL, then move your files and crates to the new drive, and finally use the 'relocate lost files' feature to locate your moved files.

Move your files to a folder on your external drive.
Next, copy or move the ScratchLIVE folder located in your Music folder (Mac, Vista) or My Music folder (XP) into the root of your external drive.

Once moved over add an underscore (_) to the beginning and end of the ScratchLIVE folder so it reads _ScratchLIVE_.

Now open SSL.

You should see all of your crate files but SSL won't be able to find your music files.

Now go into the setup screen, click on the 'library' tab, minimize your SSL screen so you can get access to your desktop, and drag
and drop the folder your files are in on your external onto the 'relocate lost files' tab.

This should calculate the new location of your files and you should be good to go.

Note: If your using version 1.8.1 or higher you can also just click the 'relocate lost file' tab to have SSL locate the files.
Keep in mind, if you relocate the files in this way, and you copied the ScratchLIVE folder to your external instead of moved it completely, you will need to rename the ScratchLIVE folder on your internal drive to something like "ScratchLIVErename".
Once SSL locates the files on your external, go back into your Music folder on your internal drive, delete the newly created ScratchLIVE folder, and rename the "ScratchLIVErename" folder back to its original "ScratchLIVE" name.

All should be well.

I hope that helps:)