Update:

Tested the machine with a monitor now. It boots into OS 9. A lot of personal data, so I guess a reinstall would be the right thing to do.

Does anybody know what software I need to install on it to make use of the PC card? It had a 1 GB disk image file on it, but I could not figure out how to boot it.

Also, mystery solved. It is a 7300/7500 series machine, according to System Profiler. No video input, so this must be a 7300 with the PC card.