As of 26June10, these instructions are out of date for fixing Mac Steam Content. See reply No.18 below or go directly to the Mac Rumors Guide.
Ok, I got it. When I get some time, I'll add it to one of the guides here at Mac Rumors. Here is a in-depth description:
This is the problem. As of 07June2010 Mac Steam insists on installing games into your documents folder in a folder called Steam Content and you don't have enough internal drive space to install games there. Here is the current work around to put these games on an external drive. This could also be done with another partition.
The idea is that by using the Mac's Terminal Application, you are going to create a new unix symbolic link in your Documents folder that points to the Steam Content folder located in another location. In my case the other location is my external drive.
Proceed at your own risk!!!
1. To start out with I wanted Mac Steam on my external drive for use with my MBP laptop, so I downloaded Mac Steam, opened the .dmg file and installed it there by simply dragging the Steam application from the .dmg file to the desired location on my external drive.
2. Launch Steam. By default it is going to automatically install the Steam Content folder in your Home>Documents Folder. Shut down Steam.
3. Locate the "Steam Content" folder in your home/Documents folder. Drag this to the new desired location, where it will be copied. Move the original Steam Content folder from your Document folder to the trash.
4. Open the Terminal application, located in your Utility folder. (In your Mac Finder along the top look for the "Go" pulldown menu> Utilities>Terminal). When you launch the Terminal a window opens that has a command line that starts with something like:
MyMac:~ jharris$ (where jharris is the user).
5. Type in this command (no quotes) "ln -s" (with a space between "ln" and "-s", followed by a space. Note the command "ln" consists of the small letters LN, not IN). Your Terminal command line should look something like this:
MyMac:~ jharris$ ln -s
6. Open the window that shows the new location of your Steam Content folder (the one you just moved). Left click on this folder and drag it to the Terminal Window then release it. This will copy the path to your Steam Content folder. Your command line should look something like this now:
MyMac:~ jharris$ ln -s /Volumes/WDMac2/Steam\ Content
(In my case "/Volumes/WDMac2/" is a partition on my external drive. The folder name is "Steam\ Content". (no quotes! The backward slash tells unix, there is a space.)
7. Open your home folder. (In your Finder along the top look for the "Go" pulldown menu> Home). There will be a "Documents" folder in your Home folder. Click on the Document's folder, drag it to the Terminal Window, and release it. The path to your Documents folder will automatically pop in with a space between it and the previous command. Your Terminal command window should now look something like this:
MyMac:~ jharris$ ln -s /Volumes/WDMac2/Steam\ Content /Users/jharris/Documents
8. On the Terminal command line you are now going to type in the name of the link that will be placed into the Documents folder (by using this Terminal command). Right after the word "Documents" type in this syntax with no space (no quotes!): "/Steam\ Content" (Put a space between "\" and "Content". The \ tells the Terminal there is a space between the words Steam and Content). Your terminal command line should now look something like this:
MyMac:~ jharris$ ln -s /Volumes/WDMac2/Steam\ Content /Users/jharris/Documents/Steam\ Content
9. Select the Terminal Window, and now hit the "Return" button. A new command line will appear that looks like:
MyMac:~ jharris$
Quit the Terminal. If you have formatted this command correctly, a new Alias of your Steam Content folder should show up in your Documents folder. Now launch Steam and see if it worked.
The easiest was to tell is when you start to download a new game, you'll get a message telling you how many MBs of space are available. This can be checked against the partition you want to install to and compare it to the available space on your internal hard drive. If things look good, start downloading games to your external hard drive!!