Try:
Belarc Advisor (free)
Everest Home Edition (free)
''Built-in'' = on its own card? Integrated into motherboard?
If the modem is on its own card, you usually find out model information from the markings. The FCC ID code on the modem can help:
http://www.fcc.gov/oet/fccid/help.html
If you find a mfg name, you can look on their site for info. Some sites have tools you can download to ID the modem.
I recently bought a new desktop-Sony Vaio VGC-RC110G and need help identifying the built in modem for an older application. The driver is paired with the audio system and starts "HDaudio..." I need to figure out the command strings.
ie dial: ATH0
hangup string and so on.
I already tried to google it with no success.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic