chmod/chown question

Dear all, I have a FAT32 partition on my disk, namely /dev/hda6, that has been mounted in defaults mode on the directory /windows/File_Sharing. The owner is root and group is root too. Well, I would like to be able to save my WinXP/Linux documents that have to be shared between the OS without being root: I know the usage of command chmod/chown, but every time I try to use this command as root on File_Sharing subdrectories, chmod -R <username>.users <dirname> or (the user belong both to users and root groups) chmod -R <username>.root <dirname> I experienxce troubles and errors like this one: OPERATION NOT PERMITTED do you have any suggestion about solving this "simple" problem?? Thanks LM