Multiplexing a print job

My client is having an instrument which directly prints throuhg LPT1. For interfacing with this instrument, he wants to capture the data that is being printed without hampering his printing facility. Can anybody suggest any means so that the data from the LPT1 can be captured in a file while the data is sent to printing. Is it possible to multiplex this print job?
Important info – a] Client is using Compaq Presario, windows 2000 professional
b] NOTHING can be done on the instrument side, since there is nobody available to manipulate the instument output.

Thanks in Advance
BNB