1433 is the default assigned number.
However, one can choose to configure it in a variety of ways.
In particular, if you are operating behind a firewall, it may have some other port.
To see the actual values, run
netstat -an
from the MS_DOS command prompt, and examine the output, to see what ports are in use.
One would typically do this while connecting to said server from some remote location, and
knowing that 'foreign address' match that with the local address, and it will show the ports.
E.g.
Proto Local Address Foreign Address State
TCP 192.168.1.100:1433 192.168.1.50:1537 ESTABLISHED
Where 192.168.1.50 is your client. This would show the SQL server is listening at 1433, on
the network interface at 192.168.1.100
Another technique would be to put some ethernet sniffer on the physical network, and watch
a transaction occur. Again, initiate from a know place, and watch/filter for that source location.
