Hello fajardo,
You can have a look at this URL to find the port numbers of applications:
http://www.iana.org/assignments/port-numbers
These are the standard ports which will be used for TCP/IP communications.
Anyway, you might have more than one ports when you access applications like active directory, file/print etc.. To find out exactly, as to which port the PC is accessing, you can run a local sniffer and track the port numbers and open the same on the PIX firewall.
Hope this helps.. all the best...
Raj
