Attribute "O"

Are you referring to a unix file system?  If so, "o" refers to group other, also known as the rest of the world, when used with the chmod command.  For example, "chmod o+r datafile" allows everyone to read this file.  The other possibilities for permissions can be user or group: http://www.tech-recipes.com/unix_tips691.html

Here are all the attributes that are listed for Wind XP, I believe you may be looking at a refrence to linux where an o means display details about the owner.

 http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/xcopy.mspx

NO, Windows.  I have files that are tagged with the "O" attribute.

The attrib command does not have an "o": http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/attrib.mspx

Where are you seeing this attribute?

When I open the directory in Windows and show the attributes column.  My files have an "A" and "O".  I know what the "A" is for but I don't know what the "O" attribute is for.

Some more info here:
http://www.febooti.com/products/filetweak/online-help/offline-file-attribute.html

"Offline file attribute specifies that file will not be physically available while working offline. When working in network environment with files stored remotely, they are only physically available while connection to this remote data storage persists. After turning off the remote computer or disconnecting portable device from the network, files stored remotely become physically unavailable.

However, with synchronization tools it is possible to create local copies of those network files. In this case files cached locally are marked offline which means that they are not original files while it is still possible to work with them."

(As to how it gets set, most synch tools utilize it, apparently. The link in the comment above links to a utility that will allow you to manually set/unset it. Sorry for comment spam!)