The only suggestion I could think of for using a web cam for security would simply be to update the process entirely where you can easily use a usb model for the same thing. When initially getting off of dsl for cable and adding on a WiFi capable router the landlord was trying to use for a wireless connection to a security system the idea of a remote desktop came to mind.
Since the cam used RJ-11 it would have needed an interface much like a dial-up modem when originally working. That would have gone into an ISA or PCI slot on the machine itself depending on just how old and if it still saw ISA that is with PCI replacing the older.
With two 7 builds here I can easily set one up with a web cam and monitor it remotely using the TeamViewer
program so I wouldn't have to be physically present at the other where the cam is added on. Take any old XP case and slap a usb cam on that and then add TeamViewer once you have the web cam working to monitor things remotely.
The little tab in TeamViewer by the way that shows on the desktop can be hidden from view by clicking on the left side. You can see that in the image attached here with the wited out spot and the tab to click on on the side of the popup.
That will not only provide a working solution but besides updating things on the OS side a little provide remote as well as machine viewing.