This was already subject in MMD some time ago.  It depends on the laptop
you use.  If the laptop PC is able to connect to a port replicator like
mine does, this is the best solution in my opinion.  My port replicator
has the same outputs as a modern desktop computer: serial, parallel,
USB, and a game port which has a MIDI IN and a MIDI OUT.  You only need
to put the connector cable (with the MIDI opto coupler in the jack)
into the game port.  You then can send and receive MIDI data from
Windows and DOS.

If your computer cannot connect to a port replicator you can use a
device which connects to the serial port, or better to the parallel
port, like the well known Midiman.  It comes with a driver at least
for Windows.  I did not like it very much so I switched to the port
replicator.

Wishing you success,
Horst Mohr