The mybook is on a 20mbit symmetric connection, but what bandwidth do you have available at the other end? 30 kb/s upload is slow for home broadband, but not unheard of.
I don’t use ftp as it’s proven more hassle than it’s worth where firewalls are concerned, so I’m inclined to think that’s where the problem lies. A network device somewhere between the NAS and the PC is causing the problem.
There’s a whole load of other potential problems though, you’ve not given enough information to take an educated guess at where the problem lies. At the very least, can you upload to other computers on the same lan at a faster speed?