Installing Gimp On MAC OS X
First Thing is first, you need X11 installed on OS X. The quickest way to accomplish this installation is to 
get the Mac OS X Install Disc 1.
Select the optional installs package from the Installation DVD a seen below:
We are interested in X11, and as a matter of being focused we will step through the installatio
n procedure. It's worth your time to become familiar with what is on this disk and I would encourage you to do so especially if your after the proper XCODE installation. For now, select X11 package from the applications Package Folder as seen below:
Click on the "Optional Installs" icon to launch the installer.
Go through the installation until the dialog highlights the Installation Type.
Choose applications and then check the X11 box to install the X11 application. This is all that is needed for GIMP to install correctly.
Click on the Install button.
If everything goes correctly, you should have success!
Now that we have that all set up we can move toward a GIMP installation. This is rather simple as the only thing really difficult was finding that OS X Disk 1 Installation. 
Download the OS X version of GIMP and there is additional documentation about installation and all things GIMP.
Now your X11'd Up and GIMP'd OUT.... Your all set for Open Office!
Could you give me a clue how to find the OS X version of GIMP. All I can
find on their web site is source code. Alternatively this post needs some
instructions on how to compile it up - or can you point me elsewhere for
this?