If it were a FAT32 property, it might be fairly easy to implment. But I suspect that it's an NTFS property. NTFS is a far superior filesystem, but it's also a lot more complicated (just look at the problems the Linux kernel has getting usable NTFS write support).

On a tangently-related subject, why is there a "do not delete" attribute, anyway? If you can write the file, you can blank it out and effecitvely delete it without actually unliking it from the filesystem. I can't imagine why you wouldn't give someone write access but would allow them to delete the file. This attribute seems completely redundant, and is almost as stupid as the "execute only" attribute in DOS.

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Reinvent a rounder wheel.

Note: All code is untested, unless otherwise stated