This is more of a Windows driver development question, and this freeware (found using google) might help you do what you want to do:

http://www.programurl.com/miraplacid-publisher-sdk.htm

Another solution which you could implement entirely is perl is to find a Windows print driver which communicates to the printer via the serial port. Then use the com0com driver to create a serial port bridge. The flow of data would be:

1. User's PC
2. connects to your printer via Windows Printer Sharing
3. talks to the printer driver
4. sends data through one end of the com-com bridge
5. arrives at your perl program which has opened up the other end of the bridge
6. which dumps the data to a file

(Rube Goldberg, EYHO.)

The com0com driver is pretty cool. You can also create com to tcp bridges which allows you to communicate with serial devices over the network.

Link to the com0com project: http://com0com.sourceforge.net/