Download:

Unofficial20DSupport.js (4kB)

To Install:
1. Copy the file Unofficial20DSupport.js to your PhotoshopCS/Presets/Scripts folder.
2. Restart Photoshop.
3. Run the script from the File/Scripts Menu.

To Uninstall:
1. Run the script again from the File/Scripts Menu. It will ask you if you want to remove Unofficial 20D support.

Warning:
This script makes a copy of the official ACR plug-in and performs a modification on the copy. It does not alter the original plug-in. If anything goes wrong in the process of writing this new copy, it may prevent you from being able to launch Photoshop. To correct the situation, you'll need to find the file 'Camera Raw Unofficial Canon 20D.8bi' in your Photoshop/Plug-Ins/File Formats folder and delete it.

Adobe does not yet officially support the Canon 20D raw files and most likely will not provide technical assistance with this.

/*
 * Written by: Thomas Fors.
 *
 * This script is free!
 *
 * I ask that if you find it useful, please contact Canon and tell them you
 * use Adobe Camera Raw for your raw conversions. Ask them to start
 * cooperating with Adobe so future Canon cameras will be supported by ACR
 * much quicker after release.
 *
 * You can contact Canon here:
 *   http://consumer.usa.canon.com/ir/controller?act=ProductInfoFormAct&fcategoryid=601
 *
 * You might also consider asking them to support a standard RAW format.
 *   http://rawformat.com
 *
 * Finally, the legal stuff..
 *
 * THIS SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

// Find the Official ACR plugin in the expected location or ask the user to help
var originalACR = File(Folder.startup + "/Plug-Ins/File Formats/Camera Raw.8bi");
if ( !originalACR.exists ) {
		if ( Folder.fs == "Windows" ) {
				originalACR = File.openDialog("Find and Select the 'Camera Raw.8bi' File", "Photoshop Plug-ins:*.8bi");
		} else if ( Folder.fs == "Macintosh" ) {
				originalACR = File.openDialog("Find and Select the 'Camera Raw.8bi' File", pluginFilter);
		}
}

// Check if hack already exists and prompt the user asking what to do
var bRemove = false;
var bProceed = false;
var newACR = File(originalACR.path + "/Camera Raw Unofficial Canon 20D.8bi");
if ( newACR.exists ) {
		bRemove = confirm("Unofficial Canon 20D support already exists.\rDo you want to remove?");
		if (bRemove) {
				newACR.remove();
				alert("Unofficial Canon 20D support has been successfully removed.\rYou should restart Photoshop.");
		}
} else {
		bProceed = confirm("Do you want to add Unofficial Canon 20D support?");
}

if ( bProceed ) {
		// Create a backup copy of the original ACR file to work with.
		originalACR.copy(newACR);

		// Read backup copy of ACR into memory
		newACR.encoding = "BINARY";
		newACR.open("r");
		var memoryACR = newACR.read();
		newACR.close();

		// Perform some sanity checks to make sure this is the ACR plug-in
		var validACR = true;
		if (!memoryACR.match(/Adobe/)) validACR = false;
		if (!memoryACR.match(/Camera Raw/)) validACR = false;
		if (!memoryACR.match(/Thomas Knoll/)) validACR = false;
		if (!memoryACR.match(/Canon EOS-1D Mark II/)) validACR = false;

		if ( validACR ) {
				// Do the hack
				var loc = memoryACR.search(/Canon EOS-1D Mark II/);
				newACR.open("e");
				newACR.seek(loc, 0);
				newACR.write("Canon EOS 20D\0");
				newACR.close();
				alert("Unofficial Canon 20D support has been added! :-)\rYou need to restart Photoshop.");
		} else {
				alert("Official ACR Plug-in not found or incorrect version found.  Cannot create Unofficial Canon 20D support. :-(");
		}
}

//===============================
// Utility function to filter
// plugin files in dialog on Mac
// platform
//===============================
function pluginFilter(f) {
		lcName = f.name;
		lcName.toLowerCase();
		if ( lcName.indexOf(".8bi") == (f.name.length - 4) ) {
				return true;
		} else if ( f instanceof Folder ) {
				return true;
		} else {
				return false;
		}
}