Phil, Thanks for the explanation. That was exactly the information I was looking for. I just wanted to make sure that you were aware of and could explain the differences in my results, and you did. Im actually surprised that windows XP fails at a function as fundamental as changing file properties. All my experiments I was doing with test copies of pics so I didn't corrupt any originals in the process. After your explanation I feel safe using your ExifTool on my pics now.

Jim, just to clarify: My file Modification times were NOT changing when using the ExifTool, but this was intentional. If you look above at the command I was using, I included the "-P" flag(that Phil also mentioned) to keep this property from changing.

Jim's comment also got me curious to see if Vista and Windows 7 corrupt as much as XP does. So I tried the same experiment on a vista and windows 7 machines and heres what I got when I MANUALLY changed the comments with those operating systems:

Windows 7
- File Modification Date/Time was changed(however, unlike XP it actually changed it to the correct current date)
- File size changed(duh) and XPComment changed(duh)
- Interoperability Index is still deleted
- Offset Schema and Padding properties are added
- Various thumbnail properties are altered

The results for Vista were the same as windows 7 except for the following:
- Vista did NOT delete the Interoperability property like win 7 did(strange)
- Vista adds an "about" property that has a hex value in it
- Vista adds a "user comment" property which is redundant to the "XPComment" property that it also adds.

So I guess in conclusion, Vista and 7 still seem to screw up the properties a little bit, but at least its not quite as bad as XP.

I will definitely only be using ExifTool for making any types of changes to my pics metadata. Thanks for making this awesome tool, Phil.