is it a card or on motherboard?
easiest is to goto control panel, system, hardware, device manager, and check the modem driver/vendor codes.
Unfortuantly Kaori, 9/10 times it's not as easy as that. The only information you get from device manager is the make and if its not installed correctly you won't know the model of the card. So if he is looking for a driver for the card, then this will not help at all.
Best way to identify hardware in any machine is to use a nice little bit of software called
Sis Sandra. Use this to run a benchmark on your machine and it will give you all the information you need for all your hardware, it will also give you driver signatures. This help identify the correct driver for your hardware, especailly when it comes to dialup modems.