This is a copy of my post elsewhere on this discussion board:
I have just successfully set up Time Machine on my MyBook World Edition II NAS. It's not so straightforward, and the information on the Western Digital support site is either unhelpful or flat-out wrong, so here's a post that will hopefully save people in a similar position a lot of time and frustration.
Here are the key facts:
1. The MyBook World Edition II NAS does support Time Machine -- if you upgrade to at least firmware Release 1.01.14 (9/29/09). See
http://www.wdc.com/wdproducts/updates/?family=mbworld. Amazingly, the Level I support people at Western Digital told me that Time Machine is not supported! I had to point him to this link.
2. MyBook World Edition II comes with a built-in user, WD_Backup, which appears to be the only user that can be used for the backup.
3. Follow the instructions here:
http://www.wdc.com/wdproducts/updates/docs/en/appletimemachine.pdf. BUT, what the instructions don't tell you is the password for that user, which Mac OS will ask you for during the Time Machine setup. On my device, it was "admin" but other posts say the password can be "backup" or "wd_backup."
4. Ignore some of the misleading statements in the Western Digital "knowledge base." For example, it says Time Machine is not supported. That used to be true but with the firmware update, is no longer true. Also, some instructions direct you to make a partition on your drive for Time Machine using Disk Utility. This is not possible, as far as I can tell, because the MyBook World Edition II shows up as a "share," not a "device" in the system, and therefore Disk Utility does not see it.
5. The reason I wanted to set up a partition, where I could limit the disk space, is that I read that Time Machine creates daily backups, with incremental versions of documents. Thus, the Time Machine backup will eventually fill up whatever space is given to it. Since I could not partition the MyBook World Edition II, what I did instead was to enable the "Quota" functionality and then put a disk quota on the WD_Backup user. I hope this will do the trick. (I have the further issue of having two Time Machine backups, one for me, one for my wife. How our Time Machines will battle it out for the disk space, I have no idea.)
I hope that the Western Digital people will create greater flexibility for Time Machine users in future firmware updates.
Anyway, hope this helped.