A sample can be found at:
http://www.o-day.net/sample/ it is called mgupdate2.jpeg.
What I did was create an image in Photoshop 5.5 (white background, nothing pretty) and entered IPTC data. I then updated the IPTC data with MediaGrid. This resulted in IPTC data both before and after the image data. I then used the ExifTool to update the IPTC data. This updated the IPTC before the image data, but not after.
We are concerned about IPTC placement due to the vast number of tools that can be used to get at it. We have not found one tool that hits all possible IPTC data places at once. This can cause a problem if a tool like MediaGrid is used to enter IPTC data information by a photographer and some data entered is classified or not for public release. When the IPTC data is "cleaned" we use photoshop or ExifTool to load data from a database. Nither of these tools deals with the IPTC data after the image data, which leaves the initial, uncleaned, data in the image. Opening a jpg file in wordpad will display this information at the bottom of the file.