I've never heard of anything that would allow even an early PowerPC PowerBook to be used as a monitor, especially with a 68K Mac. Meaning, you could use some kind of VNC application to output the video via Ethernet, but the speed on those Macs would be so slow you'd go nuts. Plus you'd need a monitor to configure the IIsi first. Never heard of doing it with SCSI. There were SCSI video output devices specifically for use with some some PowerBooks that did not have video outs, but they did not go the other way.
Brainstorming here, you might be able to configure some primitive video output hardware (card or ext.) on the IIsi with software that allows you to output the the live desktop. Then, using additional external video hardware, input the video feed into your PowerBook which would appear in a window that you could enlarge to fill the screen. Not sure about the performance, because you would be relying on the processors to both convert the video for output and re-convert for input, while running applications.
You are better off looking for a standard LCD panel. The original Apple 15" Studio Display panel works just fine with my Duo Dock (though it is not supposed to), which should be similar to the same output as the IIsi. They can be found on eBay in the $60 range. Any old VGA monitor should work too with a common DB-15 adapter as long as the sync requirements are met. Don't really know the specs of the IIsi video, but you may need to add a video card to get standard VGA.
Brainstorming here, you might be able to configure some primitive video output hardware (card or ext.) on the IIsi with software that allows you to output the the live desktop. Then, using additional external video hardware, input the video feed into your PowerBook which would appear in a window that you could enlarge to fill the screen. Not sure about the performance, because you would be relying on the processors to both convert the video for output and re-convert for input, while running applications.
You are better off looking for a standard LCD panel. The original Apple 15" Studio Display panel works just fine with my Duo Dock (though it is not supposed to), which should be similar to the same output as the IIsi. They can be found on eBay in the $60 range. Any old VGA monitor should work too with a common DB-15 adapter as long as the sync requirements are met. Don't really know the specs of the IIsi video, but you may need to add a video card to get standard VGA.