OS X normally mounts removable drives with the "noowners" option. This ignores any file ownerships on the entire volume. From "Get Info" on the drive, uncheck the "Ignore ownership on this volume" option in "Sharing & Permissions". The following article has some discussion on this. Hopefully this will help some. I'm also assuming you've formatted the drives as HFS+. FAT does not have permissions/owners.
http://www.peachpit.com/guides/content.aspx?g=mac&seqNum=256