Denial of Service - what it means is someone is spamming and attacking the POL and FFXI routers to take them offline by flooding the channels with traffic.
Odds are that some of the traffic is legit - I know I kept hitting retry yesterday for about 25 minutes before I finally got online with POL, then about 30 more minutes just to get attached to Bismarck (and start the round of "POL-0006 errors while trying to download).
Just FYI... there are servers that have smaller populations (I've got a character on one of them) and it's a little bit easier to get the update from those servers. After trying to download from Bismarck for over an hour, I thought "doh! go to the other server!" It worked, I got my update.
Good Luck!
Zuzeeque