My ADSL connection is half MB why does it only show a data rate of
approx 56kbps in the file transfer window when downloading

I believe the speed of the adsl connection is measured in bits.  The
data rate of transfer is in bytes (1 byte = 8 bits).

Also, the "data" being saved to your hard drive is encapsulated with
headers which don't count in the data download rate but may count in
the adsl speed connection.

Some related links:

http://www.danbbs.dk/~erikoest/dl_time.htm

http://compnetworking.about.com/cs/basicnetworking/f/bitsandbytes.htm
http://compnetworking.about.com/od/basicnetworkingfaqs/f/bandwidthunits.htm

thanks james_l_mar that clears up my confusion perfectly