Download speeds are normally expressed in kBytes per second, not Kbits (as is the modem - 56kbits/sec). If you have got a real connection of 56kbps through a normal analogue line then well done (although I would have to see it to believe it!).
A 'good' connection is around 50-52kbps - dividing this into bytes gives 6.5kB/s. Taking into account server speeds, latency, handshaking and contention etc., you'll probably only get 6KB/s max.