Hi,
First thing to say is: are you sure connecting by cable is the fastest way to transfer? My MacBook and iMac both have 300Mbs wifi vs. 100Mbs ethernet cable! It depends on your router of course - how fast is that via wifi? Is it g or n standard? If it's n standard then I am guessing you will be better with wifi. Use the GB ethernet port on the WD MyBook to connect to your router and then let the MacBook connect via wifi.
Then login to the WD MyBook via Safari (or any other browser) by entering http://mybooklive into the address bar.
I can't remember if there is a default owner password, I don't think so but check the documentation. I set one up for myself.
You will get a set of options from Settings, Users, Shares etc. Start with Settings - System:
Under Updates I have mine set to Automatic - lots of people are saying up to date firmware is important.
Under Alerts - I gave it an email but it has never contacted me!
Under Energy Saver - I have it turning off the harddisk when it is idle.
Under Mac Backups I have checked Time Machine! Note the share name so that you can select it in Time Machine later.
Staying with settings go to the Network tab - have a look. The defaults (incl DCHP) should be fine. I think unchecking FTP is a good idea for security sake.
Go to the Remote Access tab - this is a bit that I think may matter.
Uncheck Remote Access. Later you can set up connections to your iPad or whatever - it will be fine after the initial backup. I can watch movies on my iPad anywhere, streamed from the MyBook, its a great feature, but turn it off for the moment.
Moving to the Media tab: Uncheck Media Streaming and Uncheck iTunes Server. This is my prime suspect for slowing things down - but who knows?
Then go down the menu to Users. Several people have said that setting up a proper user rather than using Guest matters. I don't know why (not enough deep down Linux experience) but I did set up a proper user with password. I like the security aspect as much as anything. So:
Set up a user and take careful note of the username and password. If you match the user with your MacBook it will be slightly more convenient. Now you have a user go back to Shares and select the TimeMachine share. Look in the details panel and give your new user write access (click the radio button under the pencil icon). I also made the share private - so Guest will no longer work. Check Media Serving is Off - it should be.
That should be all done for setting up the MyBook.
Now go to your Mac and open the the settings for Time Machine. Click on Select Disk and look for the MyBook in the selection of disks in the lower panel. I would strongly advise encrypting the backup - it is just behind your router firewall and later you may want to open up remote access. It will take longer to create but I think it is worth it - I did a full initial encrypted 173GB backup last night in 11 hours.
That's it: turn on the Time Machine and let it get on with it.
Once the first backup is done, you can turn on the media streaming and remote access and copy movies and music to the Public share via Finder for your enjoyment elsewhere.
Hope this helps.