Rob mentioned the article on his Digital Photography Insights website, pointing readers to the Canon's Download Library for the software. To install the software, you'll need a previous version of Digital Photo Professional, or any version of either Canon's EOS Viewer Utility, File Viewer Utility, or RAW Image Converter running on your PC. (You needn't have actually used them, but one of these programs has to be on the computer for the upgrade to work). Then simply download the file from the Download Library, selecting whether you want to use it on Windows or Macintosh platforms. Hint: EOS-1D Mark II users can get the software by clicking here, then clicking the "Drivers / Software" link on that page, and then choosing their language in the resulting pop-up window.

Courtesy of Canon, you can find below a list of changes since Digital Photo Professional 1.5.0 and 1.6.0, as well as the original Digital Photo Professional 1.0.0:

Changes

1. Changes in Digital Photo Professional 1.6.1 from the previous Digital Photo Professional 1.5.0/1.6.0 are as follows
   1. The Copy Stamp Tool (to adjust images by copying and pasting some part of the image) was added.
   2. The Rename Tool (to change multiple file names at once) was added.
   3. Lines appeared in the bottom of images converted from RAW images taken with the following models when using Digital Photo Professional 1.5.0/1.6.0 on a computer with dual processors or Hyper-Threading Technology. This problem has now been fixed.
      • EOS D60
      • EOS 10D
      • EOS Kiss Digital / EOS DIGITAL REBEL / EOS 300D DIGITAL
      • EOS-1Ds Mark II
   4. Support was added for the EOS D60 and EOS Kiss Digital N / EOS DIGITAL REBEL XT / EOS 350D DIGITAL.
   5. The amount of time it takes for image thumbnails to appear has been reduced.
      
2. Changes from the Digital Photo Professional 1.0.0 are as follows:
   1. An image-cropping tool was added.
   2. A simulation function for CMYK printing was added.
      When you select a profile you want to use in your print in the [Preferences] dialog box, the image in Digital Photo Professional and the printed image will be displayed in colors based on the selected profiles. However, the profiles specified in this function will not be applied when Easy-Photo Print is used.
   3. It is now possible to transfer multiple images to any image-editing application with a single operation.
   4. In the main window Tree View Area, you can copy, locate, or delete the folders.
   5. In the RAW images adjustment tool palette, the tone curve has been changed to a log display.
   6. You can specify the printer profiles in [Color management] in the [Preferences] dialog box.
   7. When saving an image file, the image size can be specified in the [Save as] dialog box.
   8. When saving images in JPEG, you can specify the settings to embed the ICC profile in the image using the [Save as] dialog box.
   9. When saving images in TIFF, you can specify sharpness settings in the [Save as] dialog box.

Full instructions for installing the software can be found on Canon's website.