In order to enable bandwidth limitations in OS X the following can be useful. This example limits port 139/tcp and port 445/tcp to 5 MBit/s:

ipfw -f pipe flush
ipfw -f flush
ipfw add pipe 1 dst-port 139
ipfw add pipe 1 dst-port 445
ipfw pipe 1 config bw 5Mbit/s
ipfw pipe show
ipfw show

To release the limitation again the following lines do the trick:

ipfw -f pipe flush
ipfw -f flush

ipfw pipe show
ipfw show