^^you said you reinstalled...so does that mean you still have your old GW.dat file...if so copy and paste it into the new directory...if not try using the -image switch to download the entire game file from GW then you will not have to worry about it.
^lol don't worry about it, seeing that you've already dl the update. Stopping it half-way might cause the file to corrupt. Anyway "-image" is a shot cut use to download all of the gw data in one sitting. Look up on tech faqs for the instruction.
Burn .dat mean you back up the gw.dat file, yes the 3gb+ file from your gw folder on a dvd. When you need to reinstall for whatever reason just swap the .dat file out. Also work on a new pc as well.
As for how long the dl will take, that's depend on your connection.