How to cache data from network before it is sent to printer

[Raymond]

Hi Guru,

We have a LAN and printer, currently all print tasks are sent to printer
directly, now we want to set up a print server with a printer attached to it,
all the print tasks will be sent to the server instead of the printer. The
server caches the data it receives from network, some sort of GUI will be
displayed for user to select his own job to print.

I wonder if, and how, the key is for the server to listen to a port, if any,
to see if there is any data sent to it. And if yes, catch the data, cache it
in memory.
Can anybody give me a hint?

Thanks lots.