That (512KB/sec) is 2 seconds per megabyte. The file is about 2.5
gigabytes (2,500 megabytes). should take about 5,000 seconds, which is
only about 2 hours. And, indeed, on my cable modem the download was
showing about 400KB/sec, and it took a bit, but not much, over 2 hours.
My guess is that your speed is 512Kb/sec, not 512KB/sec. Eight times
slower (but still more than 10x faster than dialup).